Circularly-polarized-light extracting optical element and process of producing the same

ABSTRACT

Provided is a circularly-polarized-light-extracting optical element adapted to effectively prevent lowering of displaying quality that is brought about by the appearance of bright and dark stripes on the screen of a display even when the circularly-polarized-light-extracting optical element is placed between circular or elliptical polarizers arranged in the cross nicol disposition. The circularly-polarized-light-extracting optical element  10  includes a liquid crystal layer  12  having cholesteric regularity with liquid crystalline molecules in planar orientation. The liquid crystalline molecules on a surface  12 A, which is one of the two main opposite surfaces  12 A and  12 B of the liquid crystal layer  12,  are wholly oriented in substantially one direction (director Da) and the liquid crystalline molecules on the other main surface  12 B of the liquid crystal layer  12  are also wholly oriented in substantially one direction (director Db). In the case where the liquid crystal layer  12  is made of a plurality of liquid crystal layers, it is preferable that the directors in planes in the vicinity of the interface of each two neighboring liquid crystal layers be substantially parallel to each other.

TECHNICAL FIELD

The present invention relates to a circularly-polarized-light-extractingoptical element for use in the extraction of circularly polarized lightfrom non-polarized light by making use of a liquid crystal layer havingcholesteric regularity, to a process of producing such acircularly-polarized-light-extracting optical element, and to apolarized light source device and a liquid crystal display using such acircularly-polarized-light-extracting optical element. The term “liquidcrystal layer” as used in this specification means a layer having theproperties of liquid crystals in an optical sense; and, from theviewpoint of the state of the layer, the “liquid crystal layer” includesa layer in the state of fluid liquid crystalline phase, as well as alayer in the state solidified with the molecular orientationcharacteristic of a liquid crystalline phase maintained.

BACKGROUND ART

A circularly-polarized-light-extracting optical element that is made toreflect either right- or left-handed circularly polarized componenthaving a wavelength equal to the helical pitch of liquid crystallinemolecules in a cholesteric liquid crystal layer and to transmit theother circularly polarized component has conventionally been known as anoptical element using a cholesteric liquid crystal or the like.

To extract (selectively reflect) circularly polarized component in abroadened wave range, there has been proposed acircularly-polarized-light-extracting optical element composed of alaminate of a plurality of cholesteric liquid crystal layers havingdifferent pitches of liquid crystalline molecular helixes (JapaneseLaid-Open Patent Publications No. 271731/1996 and No. 264907/1999).Further, Japanese Laid-Open Patent Publication No. 304770/1997, forexample, discloses a polarized light source device and a liquid crystaldisplay each containing such a circularly-polarized-light-extractingoptical element.

The circularly-polarized-light-extracting optical element as describedabove is often used as a display member. As shown in FIG. 21, thecircularly-polarized-light-extracting optical element 203 is oftenplaced between circular polarizers (or elliptical polarizers) 201 and202 arranged in the cross nicol disposition (combination of aright-handed circular polarizer and a left-handed circular polarizer),for example.

In the case where the circularly-polarized-light-extracting opticalelement is used as a display member in the above-described manner, it isnecessary that the condition of polarization be uniform throughout thelight-emitting surface of the display. It has been, however, found thatbright and dark stripes can appear on the screen of a display todrastically lower the displaying quality of the display.

Through experiments and computer-aided simulations, we have made earneststudies to clear up the cause of the above-described phenomenon; and, asa result, we have found that this phenomenon occurs depending partly onthe direction (director) in which liquid crystalline molecules areoriented on the surface of a circularly-polarized-light-extractingoptical element.

In connection with the above phenomenon, we have also found thefollowing: a circularly-polarized-light-extracting optical element madeby laminating a plurality of cholesteric liquid crystal layers showslowered optical activity depending partly on the constitution of thelaminate of the two or more cholesteric liquid crystal layers; and, inparticular, in the case where a cholesteric liquid crystal layer isdirectly applied to another cholesteric liquid crystal layer, thedirectors in planes in the vicinity of the interface of the twoneighboring cholesteric liquid crystal layers are significant.

In a conventional circularly-polarized-light-extracting optical elementas disclosed in Japanese Laid-Open Patent Publication No. 264907/1999, aplurality of cholesteric liquid crystal layers that have been made intofilms in advance are usually adhered either with an adhesive orthermally without using any adhesive.

In the case where an adhesive is used, the adhesion between the liquidcrystalline molecules in the liquid crystal layer that has been madeinto a film and the molecules of the adhesive is required to be good.Therefore, not only the types of adhesives that can be used are limited,but also the resulting circularly-polarized-light-extracting opticalelement inevitably has a thickness increased by the thickness of theadhesive layer. In addition, the use of an adhesive brings such problemsthat reflection occurs at the interface of the adhesive layer and theliquid crystal layer due to the difference in refractive index betweenthe two layers and that light extracted by thecircularly-polarized-light-extracting optical element has the color ofthe adhesive layer itself.

In the case where liquid crystal layers are thermally adhered withoutusing any adhesive, it is necessary to heat the liquid crystal layersthat have been made into films to temperatures equal to or higher thantheir glass transition temperatures (Tg) to soften them.Industrialization of this method is therefore difficult from theviewpoints of the constitution of apparatus for thermal adhesion andhandling. In addition, the liquid crystalline molecules in a liquidcrystal layer and those in the neighboring liquid crystal layer arerandomly intermingled when the liquid crystal layers are heated to hightemperatures, causing deterioration of the optical properties.

Furthermore, whether an adhesive is used or not, it is necessary toemploy an alignment layer and a substrate in order to align liquidcrystalline molecules in the state of planar orientation. The resultingcircularly-polarized-light-extracting optical element therefore has athickness increased by the thickness of the alignment layer and that ofthe substrate. If an aligned film such as an oriented PET (polyethyleneterephthalate) film is used as a substrate, it is possible to omit analignment layer because the aligned film itself also serves as analignment layer. Even in this case, the resultingcircularly-polarized-light-extracting optical element has a thicknessincreased by the thickness of the aligned film. It seems effective thatthe alignment layer and the substrate are separated after the liquidcrystal has been solidified. In this case, however, the liquid crystallayers are often damaged upon separation of the alignment layer and thesubstrate, decreasing the mass-productivity. Moreover, in the case wherethree or more liquid crystal layers are laminated, any of theabove-described methods becomes considerably complicated; and, inaddition, the substrates and the alignment layers in a number equal tothe number of the liquid crystal layers are wasted.

In order to overcome these problems, there has been proposed such amethod that a circularly-polarized-light-extracting layer is formed bycoating a cholesteric liquid crystalline polymer layer with anothercholesteric liquid crystalline polymer, as disclosed in JapaneseLaid-Open Patent Publication No. 44816/1999.

This method is, however, disadvantageous in that it is difficult toalways make the helical axes of cholesteric liquid crystalline moleculesin the liquid crystal layers constant. Moreover, since a cholestericliquid crystalline polymer is simply applied in the above method, theliquid crystalline molecules existing in the vicinity of the interfaceof two neighboring cholesteric liquid crystalline polymer layers are notoriented in one direction, and discontinuity is thus created in directorat the interface of the two cholesteric liquid crystalline polymerlayers. For this reason, the resultingcircularly-polarized-light-extracting optical element shows loweredoptical activity.

DISCLOSURE OF THE INVENTION

The present invention has been accomplished by taking the aforementioneddrawbacks into consideration. A first object of the present invention isto provide a circularly-polarized-light-extracting optical elementadapted to effectively prevent lowering of displaying quality that isbrought about by bright and dark stripes that appear on the screen of adisplay even when the circularly-polarized-light-extracting opticalelement is placed between circular or elliptical polarizers arranged inthe cross nicol disposition; a process of producing such acircularly-polarized-light-extracting optical element; a polarized lightsource device using the circularly-polarized-light-extracting opticalelement; and a liquid display using thecircularly-polarized-light-extracting optical element.

A second object of the present invention is to provide acircularly-polarized-light-extracting optical element adapted toextracting circularly polarized light over a continuous selectivereflection wave range having no optical singularity even if it isproduced by laminating a plurality of liquid crystal layers; a processof producing such a circularly-polarized-light-extracting opticalelement; a polarized light source device using thecircularly-polarized-light-extracting optical element; and a liquiddisplay using the circularly-polarized-light-extracting optical element.

A first circularly-polarized-light-extracting optical element accordingto the first feature of the present invention comprises a liquid crystallayer having cholesteric regularity with liquid crystalline molecules inplanar orientation, wherein the liquid crystalline molecules on one ofthe two main opposite surfaces of the liquid crystal layer are whollyoriented in substantially one direction (director) and the liquidcrystalline molecules on the other main surface of the liquid crystallayer are also wholly oriented in substantially one direction(director).

In this circularly-polarized-light-extracting optical element, it ispreferable that the director on one of the two main opposite surfaces ofthe liquid crystal layer be substantially parallel to that on the othermain surface of the liquid crystal layer. The expression “substantiallyparallel” herein means that the discrepancy between the two directors iswithin the range of ±20°. It is also preferable that a helical structureconsisting of liquid crystalline molecules with helical turns in anumber of (0.5×integer) be present between the liquid crystallinemolecules existing on the two main opposite surfaces of the liquidcrystal layer.

A second circularly-polarized-light-extracting optical element accordingto the first feature of the present invention comprises a plurality ofliquid crystal layers having cholesteric regularity with liquidcrystalline molecules in planar orientation, the liquid crystal layersbeing successively and directly laminated, wherein the liquid crystalline molecules on one of the two main opposite outermost surfaces of theliquid crystal layers laminated are wholly oriented in substantially onedirection (director) and the liquid crystalline molecules on the othermain outermost surface of the liquid crystal layers laminated are alsowholly oriented in substantially one direction (director).

In this circularly-polarized-light-extracting optical element, it ispreferable that the director on one of the two main opposite outermostsurfaces of the liquid crystal layers laminated be substantiallyparallel to that on the other main outermost surface of the liquidcrystal layers laminated. The expression “substantially parallel” hereinmeans that the discrepancy between the two directors is within the rangeof ±20°. It is also preferable that a helical structure consisting ofliquid crystalline molecules with helical turns in a number of(0.5×integer) be present between the liquid crystalline moleculesexisting on the two main opposite outermost surfaces of the liquidcrystal layers laminated. Moreover, it is preferable that the directorsin planes in the vicinity of the interface of each two neighboringliquid crystal layers of the multiple liquid crystal layers laminated besubstantially parallel to each other. The expression “substantiallyparallel” herein means that the discrepancy between the two directors iswithin the range of ±5°.

A first process of producing a circularly-polarized-light-extractingoptical element according to the first feature of the present inventioncomprises the steps of coating an alignment layer whose entire surfacehas been treated so that its alignment-regulating action will act insubstantially one direction, with liquid crystalline moleculescomprising polymerizable monomer or oligomer molecules havingcholesteric regularity, so as to align the liquid crystalline moleculesby the alignment-regulating action of the alignment layer;three-dimensionally crosslinking the liquid crystalline molecules thathave been aligned by the alignment-regulating action of the alignmentlayer, thereby forming a first liquid crystal layer; directly coatingthe first liquid crystal layer with another liquid crystalline moleculescomprising polymerizable monomer or oligomer molecules havingcholesteric regularity, so as to align the liquid crystalline moleculesby the alignment-regulating action of the surface of the first liquidcrystal layer that has been three-dimensionally crosslinked; andthree-dimensionally crosslinking the liquid crystalline molecules thathave been aligned by the alignment-regulating action of the surface ofthe three-dimensionally crosslinked first liquid crystal layer, therebyforming a second liquid crystal layer. In this production process, it ispreferable to adjust the thickness of the first liquid crystal layer andthat of the second liquid crystal layer so that the directors on the twomain opposite surfaces of the first liquid crystal layer will besubstantially parallel to each other and that the directors on the twomain opposite surfaces of the second liquid crystal layer will besubstantially parallel to each other. It is also preferable that, in thestep of coating the alignment layer with the liquid crystallinemolecules and aligning these liquid crystalline molecules to form thefirst liquid crystal layer, the alignment of the liquid crystallinemolecules on the surface of the first liquid crystal layer be regulatedby applying another alignment layer to the surface of the first liquidcrystal layer at the opposite of the firstly provided alignment layer.

A second process of producing a circularly-polarized-light-extractingoptical element according to the first feature of the present inventioncomprises the steps of coating an alignment layer whose entire surfacehas been treated so that its alignment-regulating action will act insubstantially one direction, with a liquid crystalline polymer havingcholesteric regularity, so as to align the liquid crystalline polymer bythe alignment-regulating action of the alignment layer; cooling theliquid crystalline polymer that has been oriented by thealignment-regulating action of the alignment layer to transform it intothe glassy sate, thereby forming a first liquid crystal layer; directlycoating the first liquid crystal layer with another liquid crystallinepolymer having cholesteric regularity, so as to align the liquidcrystalline polymer by the alignment-regulating action of the surface ofthe first liquid crystal layer that has been transformed into the glassystate; and cooling the liquid crystalline polymer that has been alignedby the alignment-regulating action of the surface of the first liquidcrystal layer in the glassy state to transform it into the glassy state,thereby forming a second liquid crystal layer. In this productionprocess, it is preferable to adjust the thickness of the first liquidcrystal layer and that of the second liquid crystal layer so that thedirectors on the two main opposite surfaces of the first liquid crystallayer will be substantially parallel to each other and that thedirectors on the two main opposite surfaces of the second liquid crystallayer will be substantially parallel to each other. It is alsopreferable that, in the step of coating the alignment layer with theliquid crystal line polymer and aligning the liquid crystalline polymerto form the first liquid crystal layer, the alignment of the liquidcrystalline polymer on the surface of the first liquid crystal layer beregulated by applying another alignment layer to the surface of thefirst liquid crystal layer at the opposite of the firstly providedalignment layer.

A polarized light source device according to the first feature of thepresent invention comprises: a light source; and the above-describedcircularly-polarized-light-extracting optical element, which receiveslight emitted from the light source and transmits polarized light.

A liquid crystal display according to the first feature of the presentinvention comprises: the above-described polarized light source device;and a liquid crystal cell which receives polarized light emitted fromthe polarized light source device and transmits the polarized lightwhile changing the transmittance for it.

According to the first feature of the present invention, the liquidcrystal line molecules on one of the two main opposite surfaces of aliquid crystal layer are wholly oriented in substantially one directionand the liquid crystalline molecules on the other main surface of theliquid crystal layer are also wholly oriented in substantially onedirection. Therefore, even in the case where the resultingcircularly-polarized-light-extracting optical element is placed betweencircular or elliptical polarizers arranged in the cross nicoldisposition, it is possible to effectively prevent lowering ofdisplaying quality that is caused by the appearance of bright and darkstripes on the screen of a display.

Further, by making the director on one of the two main opposite surfacesof the liquid crystal layer substantially parallel to that on the othermain surface, it is possible to more effectively prevent the appearanceof bright and dark stripes.

A first circularly-polarized-light-extracting optical element accordingto the second feature of the present invention comprises a plurality ofliquid crystal layers having cholesteric regularity, wherein the liquidcrystal layers are laminated so that the helical axes of the liquidcrystalline molecules will point in substantially one direction, and thedirectors in planes in the vicinity of the interface of each twoneighboring liquid crystal layers of the multiple liquid crystal layerslaminated substantially coincide with each other. In thiscircularly-polarized-light-extracting optical element, it is preferablethat each liquid crystal layer comprises either polymerizable monomer oroligomer molecules that have been three-dimensionally crosslinked, or aliquid crystalline polymer.

In this circularly-polarized-light-extracting optical element, at leastone of the multiple liquid crystal layers has a pitch of the molecularhelix in the helical structure consisting of liquid crystallinemolecules, different from that of the molecular helix in the helicalstructure in the other liquid crystal layers.

It is also preferable that the thickness of each liquid crystal layer besmaller than the thickness required for the liquid crystal layer toreflect, with a maximum reflectance, either right-handed or left-handedcircularly polarized component of light having a specific wavelength,contained in incident light.

It is also preferable that the directions of rotation of the liquidcrystalline molecules in the respective liquid crystal layers be thesame. It is also preferable that at least two of the multiple liquidcrystal layers have selective reflection wave ranges whose centerregions do not agree with each other and whose end regions are partiallyoverlapped.

A second circularly-polarized-light-extracting optical element accordingto the second feature of the present invention comprises: a plurality ofliquid crystal layers having cholesteric regularity; and a transitionliquid crystal layer provided between at least any two neighboringliquid crystal layers of the multiple liquid crystal layers, in whichthe pitch of the molecular helix in the helical structure consisting ofliquid crystalline molecules varies in the direction of thickness,wherein the liquid crystal layers are laminated so that the helical axesof the liquid crystalline molecules will point in substantially onedirection; the directors in planes in the vicinity of the interface ofeach two neighboring liquid crystal layers of the multiple liquidcrystal layers substantially coincide with each other; the pitch of themolecular helix in one of the two liquid crystal layers between whichthe transition liquid crystal layer is provided is different from thatof the molecular helix in the other liquid crystal layer; and the pitchof the molecular helix on one surface of the transition liquid crystallayer is substantially equal to that of the molecular helix in theliquid crystal layer which is in contact with one surface of thetransition liquid crystal layer, while the pitch of the molecular helixon the other surface of the transition liquid crystal layer issubstantially equal to that of the molecular helix in the other liquidcrystal layer which is in contact with the other surface of thetransition liquid crystal layer.

A first process of producing a circularly-polarized-light-extractingoptical element according to the second feature of the present inventioncomprises the steps of: coating an alignment layer with liquidcrystalline molecules comprising polymerizable monomer or oligomermolecules having cholesteric regularity, so as to align the liquidcrystalline molecules by the alignment-regulating action of thealignment layer; three-dimensionally crosslinking the liquid crystallinemolecules that have been aligned by the alignment-regulating action ofthe alignment layer, thereby forming a first liquid crystal layer;directly coating the first liquid crystal layer with another liquidcrystalline molecules comprising polymerizable monomer or oligomermolecules having cholesteric regularity, so as to align the liquidcrystalline molecules by the alignment-regulating action of the surfaceof the first liquid crystal layer that has been three-dimensionallycrosslinked; and three-dimensionally crosslinking the liquid crystallinemolecules that have been aligned by the alignment-regulating action ofthe surface of the three-dimensionally crosslinked first liquid crystallayer, thereby forming a second liquid crystal layer.

A second process of producing a circularly-polarized-light-extractingoptical element according to the second feature of the present inventioncomprises the steps of: coating an alignment layer with a liquidcrystalline polymer having cholesteric regularity, so as to align theliquid crystalline polymer by the alignment-regulating action of thealignment layer; cooling the liquid crystalline polymer that has beenaligned by the alignment-regulating action of the alignment layer totransform it into the glassy sate, thereby forming a first liquidcrystal layer; directly coating the first liquid crystal layer withanother liquid crystalline polymer having cholesteric regularity, so asto align the liquid crystalline polymer by the alignment-regulatingaction of the surface of the first liquid crystal layer that has beentransformed into the glassy state; and cooling the liquid crystallinepolymer that has been aligned by the alignment-regulating action of thesurface of the first liquid crystal layer in the glassy state totransform it into the glassy state, thereby forming a second liquidcrystal layer.

A polarized light source device according to the second feature of thepresent invention comprises: a light source; and the above-describedcircularly-polarized-light-extracting optical element, which receiveslight emitted from the light source and transmits polarized light.

A liquid crystal display according to the second feature of the presentinvention comprises: the above-described polarized light source device;and a liquid crystal cell that receives polarized light emitted from thepolarized light source device and transmits the polarized light whilechanging the transmittance for it.

According to the second feature of the present invention, the directorsin planes in the vicinity of the interface of each two neighboringliquid crystal layers of multiple liquid crystal layers substantiallycoincide with each other. Therefore, even if acircularly-polarized-light-extracting optical element is obtained bylaminating a plurality of liquid crystal layers, it is possible to fullybring out the property of reflecting circularly polarized lightcharacteristic of the cholesteric structure and to obtain circularlypolarized light over a continuous selective reflection wave range havingno optical singularity. Namely, if the directors do not substantiallycoincide with each other, optical singularity is created. Therefore,when the spectral reflectance is measured by the use of circularlypolarized light, discontinuity is found in the selective reflectionwavelength. In particular, by directly coating a firstly formed liquidcrystal layer whose surface has aligning action, with another liquidcrystal layer to align, by this aligning action, the liquid crystallinemolecules in the liquid crystal layer secondly formed, it is possible toeasily make the directors in planes in the vicinity of the interface ofthe two neighboring liquid crystal layers substantially coincide witheach other.

If the liquid crystal layers are made so that the pitches of themolecular helixes in the respective liquid crystal layers are differentfrom each other, it is possible to extract circularly polarizedcomponent of light having any desired wavelength.

In particular, if the thickness of each liquid crystal layer is madesmaller than the thickness required for the liquid crystal layer toreflect, with a maximum reflectance, either right-handed or left-handedcircularly-polarized component of light having a specific wavelength,contained in incident light so that this circularly polarized componentwill be reflected with a reflectance lower than the maximum reflectance,the resulting circularly-polarized-light-extracting optical element canbe used in various optical devices with which this circularly polarizedcomponent can be extracted with a desired reflectance or transmittance.

If the directions of rotation of the liquid crystalline molecules in therespective liquid crystal layers are made identical, it is possible toavoid the formation of optical discontinuity between the liquid crystallayers.

In particular, if a circularly-polarized-light-extracting opticalelement contains at least two liquid crystal layers having selectivereflection wave ranges whose center wavelengths are different from eachother, the optical element can have a continuous, broadened selectivereflection wave range.

If a transition liquid crystal layer in which the pitch of the molecularhelix varies in the direction of thickness is provided between each twoliquid crystal layers, the resultingcircularly-polarized-light-extracting optical element can have smoothoptical properties.

In the aforementioned first and second features, polymerizable monomeror oligomer molecules that can be three-dimensionally crosslinked, aswell as liquid crystalline polymers may be used to form the liquidcrystal layers. These materials will be explained in detail in thefollowing description of embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings,

FIG. 1 is an enlarged perspective view diagrammatically showing a partof a circularly-polarized-light-extracting optical element according tothe first example of the first embodiment of the present invention;

FIG. 2 is an enlarged perspective view diagrammatically showing a partof a circularly-polarized-light-extracting optical element according tothe second example of the first embodiment of the present invention;

FIGS. 3A, 3B and 3C are diagrammatical views showing the relationshipbetween helical pitch in a helical structure consisting of liquidcrystal line molecules having cholesteric regularity and directors onthe surfaces of a liquid crystal layer;

FIG. 4 is a diagrammatical cross-sectional view illustrating a firstprocess of producing a circularly-polarized-light-extracting opticalelement according to the first embodiment of the present invention;

FIG. 5 is a diagrammatical cross-sectional view illustrating a variationof the first process of producing acircularly-polarized-light-extracting optical element according to thefirst embodiment of the present invention;

FIG. 6 is a diagrammatical cross-sectional view illustrating a secondprocess of producing a circularly-polarized-light-extracting opticalelement according to the first embodiment of the present invention;

FIG. 7 is a diagrammatical cross-sectional view illustrating a firstprocess of producing a multi-layeredcircularly-polarized-light-extracting optical element according to thefirst embodiment of the present invention;

FIG. 8 is a diagrammatical view showing the directors in planes in thevicinity of the interface of two neighboring liquid crystal layers in amulti-layered circularly-polarized-light-extracting optical elementaccording to the first embodiment of the present invention;

FIG. 9 is a diagrammatical cross-sectional view illustrating a secondprocess of producing a multi-layeredcircularly-polarized-light-extracting optical element according to thefirst embodiment of the present invention;

FIG. 10A is a diagrammatical cross-sectional view showing a polarizedlight source device comprising a circularly-polarized-light-extractingoptical element according to the first embodiment of the presentinvention;

FIG. 10B is a diagrammatical cross-sectional view showing a liquidcrystal display comprising a circularly-polarized-light-extractingoptical element according to the first embodiment of the presentinvention;

FIG. 11 is an enlarged diagrammatical view showing acircularly-polarized-light-extracting optical element according to thefirst example of the second embodiment of the present invention;

FIGS. 12A and 12B are diagrammatical views showing the directors in thecircularly-polarized-light-extracting optical element according to thefirst example of the second embodiment of the present invention;

FIG. 13 is a diagrammatical cross-sectional view illustrating a firstprocess of producing a circularly-polarized-light-extracting opticalelement according to the second embodiment of the present invention;

FIG. 14 is a diagrammatical cross-sectional view illustrating a secondprocess of producing a circularly-polarized-light-extracting opticalelement according to the second embodiment of the present invention;

FIG. 15 is an enlarged diagrammatical view showing an essential part ofthe circularly-polarized-light-extracting optical element according tothe second example of the second embodiment of the present invention;

FIG. 16 is an enlarged diagrammatical cross-sectional view showing acircularly-polarized-light-extracting optical element according to thethird example of the second embodiment of the present invention;

FIG. 17 is an enlarged diagrammatical cross-sectional view showing acircularly-polarized-light-extracting optical element according to thefourth example of the second embodiment of the present invention;

FIG. 18 is an enlarged diagrammatical view showing an essential part ofthe circularly-polarized-light-extracting optical element according tothe fifth example of the second embodiment of the present invention;

FIG. 19 is a graph showing the selective reflection wave range of thecircularly-polarized-light-extracting optical element according to thesecond example of the second embodiment of the present invention;

FIG. 20A is a diagrammatical cross-sectional view showing a polarizedlight source device comprising the circularly-polarized-light-extractingoptical element according to the second embodiment of the presentinvention;

FIG. 20B is a diagrammatical cross-sectional view showing a liquidcrystal display comprising the circularly-polarized-light-extractingoptical element according to the second embodiment of the presentinvention; and

FIG. 21 is an exploded diagrammatical perspective view showing thearrangement of a circularly-polarized-light-extracting optical elementat the time when the circularly-polarized-light-extracting opticalelement is observed by placing it between two polarizers.

BEST MODE FOR CARRYING OUT THE INVENTION

By referring to the accompanying drawings, embodiments of the presentinvention will be described hereinafter.

First Embodiment

The first embodiment of the present invention will be described byreferring to FIG. 1 to FIG. 10B.

A circularly-polarized-light-extracting optical element 10 according tothe first example of this embodiment will firstly be described byreferring to FIG. 1.

As shown in FIG. 1, this circularly-polarized-light-extracting opticalelement 10 includes a liquid crystal layer 12 having cholestericregularity (cholesteric structure) with liquid crystalline molecules inplanar orientation. The liquid crystalline molecules on a surface 12A,which is one of the two main opposite surfaces (larger surfaces) 12A and12B of the liquid crystal layer 12, are wholly oriented in substantiallyone direction (director Da) and the liquid crystalline molecules on theother main surface 12B of the liquid crystal layer 12 are also whollyoriented in substantially one direction (director Db).

In general, the liquid crystal layer 12 having cholesteric regularityhas the rotated-light-selecting property (polarized-light-separatingproperty), that is, the property of separating a component opticallyrotated (circularly polarized) in one direction from a componentoptically rotated in the opposite direction according to the physicalorientation (planar orientation) of the liquid crystalline molecules inthe liquid crystal layer.

Natural light (non-polarized light) entering into such a liquid crystallayer 12 having cholesteric regularity along the helical axis of theplanar orientation is split into two circularly polarized components,that is, right-handed circularly polarized component and left-handedcircularly polarized component; one of these circularly polarizedcomponents is transmitted and the other one is reflected. Thisphenomenon is known as circular dichroism. If the direction of rotationof the liquid crystalline molecules constituting a helical structure isproperly selected, the component circularly polarized in the samedirection as this direction of rotation is selectively reflected.

In this case, the scattering of rotated light becomes maximum at thewavelength λ₀ defined by the following equation (1):λ0=nav·p  (1)wherein p is a helical pitch of a liquid crystalline molecular helix ina helical structure, and nav is a mean refractive index in a planeperpendicular to the helical axis.

Further, the waveband width Δλ of the reflected light is represented bythe following equation (2):Δλ=Δn·p  (2)wherein Δn is an index of double refraction.

Namely, with respect to non-polarized light incident on such a liquidcrystal layer 12 having cholesteric regularity, either right- orleft-handed circularly polarized component of light in a wave range witha center wavelength λ₀, having a waveband width Δλ is reflected, and theother circularly polarized component and light (non-polarized light) ina wave range excluding the reflection wave range are transmitted. Uponreflection, the right- or left-handed circularly polarized component isreflected as it is without undergoing inversion of phase unlike in thecase of ordinary reflection of light.

The liquid crystalline molecules are oriented in substantially onedirection (director Da) on the entire surface 12A and in substantiallyone direction (director Db) on the entire surface 12B. The expression“the molecules are oriented in substantially one direction (director)”(or “directors substantially coincide with each other”) as used in thisspecification includes the case where the directions in which liquidcrystalline molecules are oriented are different by an angle ofapproximately 180°, that is, such a case that heads and tails of liquidcrystalline molecules are in the same direction. This is because, inmany cases, the head of a liquid crystalline molecule is opticallyindistinguishable from its tail. The same is true for the case whichwill be described later (the case where the director Da on the surface12A and the director Db on the surface 12B are substantially parallel toeach other).

Whether or not the liquid crystalline molecules are oriented insubstantially one direction (director Da and Db) can be known byobserving the cross section of the liquid crystal layer 12 by atransmission electron microscope. Specifically, when the cross sectionof the liquid crystal layer 12 having cholesteric regularity, in whichliquid crystalline molecules are solidified, is observed by atransmission electron microscope, bright and dark stripes are observedcorresponding to the pitch of the molecular helix characteristic of thecholesteric structure. If the bright and dark stripes that appear on thesurface 12A or 12B are seen uniformly in terms of concentration, it canbe judged that the liquid crystalline molecules on this surface areoriented in substantially one direction.

Next, by referring to FIG. 2, a circularly-polarized-light-extractingoptical element 20 according to the second example of this embodimentwill be described.

As shown in FIG. 2, the circularly-polarized-light-extracting opticalelement 20 includes a liquid crystal layer 22 having cholestericregularity with liquid crystalline molecules in planar orientation. Theliquid crystalline molecules on a surface 22A, which is one of the twomain opposite surfaces (larger surfaces) 22A and 22B of the liquidcrystal layer 22, are wholly oriented in substantially one direction(director Da) and the liquid crystalline molecules on the other mainsurface 22B of the liquid crystal layer 22 are also wholly oriented insubstantially one direction (director Db). In addition, the director Daon the main surface 22A and the director Db on the main surface 22B aresubstantially parallel to each other. The expression “substantiallyparallel” herein means that the discrepancy between the director Da andthe director Db is within the range of ±20°.

In this circularly-polarized-light-extracting optical element 20, inorder to orient the liquid crystalline molecules in precisely onedirection (director Da and Db) on each one of the two opposite surfaces22A and 22B, it is preferable that the thickness of the liquid crystallayer 20 be made (½×integer) times the pitch of the molecular helix inthe helical structure consisting of the liquid crystalline molecules. Ifthe thickness of the liquid crystal layer 20 is so made, the thicknesscan optically be divided without a remainder by a value equal to thehalf of the pitch p of the helix of the liquid crystalline moleculeshaving cholesteric regularity, as diagrammatically shown in FIGS. 3A, 3Band 3C. There can thus be prevented optical deviation from theabove-described simplified theoretical equation (1), in particular,disorder of the state of polarization that occurs due to difference inphase shift.

To form the liquid crystal layers 12 and 22 of thecircularly-polarized-light-extracting optical elements 10 and 20,polymerizable monomers or oligomers that can be three-dimensionallycross-linked, as well as liquid crystalline polymers can be used.

Examples of three-dimensionally crosslinkable, polymerizable monomersuseful for forming the liquid crystal layers include liquid crystallinemonomers and mixtures of chiral compounds as disclosed in JapaneseLaid-Open Patent Publication No. 258638/1995 and Published JapaneseTranslation No. 508882/1998 of PCT International Publication. Examplesof polymerizable oligomers that can be used to form the liquid crystallayers include cyclic organopolysiloxane compounds having cholestericphases as disclosed in Japanese Laid-Open Patent Publication No.165480/1982. By “three-dimensional crosslinking” is herein meant thatpolymerizable monomer or oligomer molecules are three-dimensionallypolymerized to give a network structure. If such a network structure isformed, the liquid crystalline molecules in the cholesteric liquidcrystalline state are optically fixed as they are, and a film that iseasy to handle as an optical film and that is stable at normaltemperatures can be obtained.

Examples of liquid crystalline polymers useful for forming the liquidcrystal layers include polymers having mesogen group, which makes thepolymers liquid crystalline, in their main chain or side chains, or bothmain chain and side chains, polymeric cholesteric liquid crystals havingcholesteryl group in their side chains, and liquid crystalline polymersas disclosed in Japanese Laid-Open Patent Publications No. 133810/1997and No. 293252/1999.

Next, processes of producing the circularly-polarized-light-extractingoptical elements 10 and 20 according to this embodiment, having theabove-described constitutions will be described hereinafter.

(First Production Process)

First of all, a production process in which a polymerizable monomer oroligomer is used for forming a liquid crystal layer will be described byreferring to FIGS. 4(A) to 4(C).

In this production process, an alignment layer 16 is firstly formed on aglass substrate 14, as shown in FIG. 4(A). Polymerizable monomermolecules (or polymerizable oligomer molecules) 18 are then applied asliquid crystalline molecules to the alignment layer 16, as shown in FIG.4(B), thereby aligning these molecules by the alignment-regulatingaction of the alignment layer 16. The polymerizable monomer (orpolymerizable oligomer) 18 thus forms a liquid crystal phase.

Next, polymerization of the polymerizable monomer (or polymerizableoligomer) 18 is initiated with the molecular orientation maintained, byapplying ultraviolet light with a photopolymerization initiator beingadded in it, or is directly initiated by applying an electron beam, asshown in FIG. 4(C), thereby three-dimensionally crosslinking(polymerizing) and solidifying the polymerizable monomer (orpolymerizable oligomer) 18. A circularly-polarized-light-extractingoptical element 10 composed of a single liquid crystal layer is thusobtained.

In the above process, if the alignment layer 16 is wholly treated inadvance so that its alignment-regulating action will act insubstantially one direction, it is possible to align, in substantiallyone direction, those liquid crystalline monomers that are brought incontact with the alignment layer 16. To align the liquid crystallinemolecules on the entire surface 12A, which is in contact with thealignment layer 16, in substantially one direction (director Da) and toalign the liquid crystal line molecules on the entire surface 12B at theopposite of the surface 12A in substantially one direction (directorDb), as shown in FIG. 1, it is enough to make the thickness of theliquid crystal layer 12 uniform. Further, in a series of the steps shownin FIGS. 4(A) to 4(C), after the step of coating the alignment layer 16with the polymerizable monomer molecules (or polymerizable oligomermolecules) 18 and before the step of three-dimensionally crosslinkingthese molecules, the following step may be added: as shown in FIGS. 5(A)to 5(D), a second alignment layer 16A is laid on the polymerizablemonomer molecules (or polymerizable oligomer molecules) 18 applied (FIG.5(C)), and ultraviolet light or an electron beam is applied, like in thestep shown in FIG. 4(C), to three-dimensionally cross-link thepolymerizable monomer molecules (or polymerizable oligomer molecules) 18sandwiched between the alignment layer 16 and the second alignment layer16A (FIG. 5(D)). In this case, to obtain acircularly-polarized-light-extracting optical element 20 as shown inFIG. 2, it is necessary to make the direction in which thealignment-regulating action of the second alignment layer 16A acts equalto that in which the alignment-regulating action of the alignment layer16 acts. Further, the second alignment layer 16A may be separated fromthe liquid crystal layer after the application of ultraviolet light oran electron beam.

The polymerizable monomer (or polymerizable oligomer) 18 may be madeinto a coating liquid by dissolving it in a solvent. If such a coatingliquid is used, it is necessary to add the drying step of evaporatingthe solvent before the step of three-dimensionally crosslinking thepolymerizable monomer (or polymerizable oligomer) 18 by the applicationof ultraviolet light or an electron beam.

In the case where the polymerizable monomer (or polymerizable oligomer)18 is made into a liquid crystal layer at a prescribed temperature, theliquid crystal layer is nematic. If any chiral agent is added to thisnematic liquid crystal, a chiral nematic liquid crystal (cholestericliquid crystal) can be obtained. Specifically, it is preferable to add achiral agent to the polymerizable monomer or oligomer in an amount ofseveral to 10%. By varying the chiral power by changing the type of thechiral agent to be added, or by varying the concentration of the chiralagent, it is possible to control the selective reflection wave range,which is determined by the cholesteric structure of the polymerizablemonomer or oligomer.

The alignment layer 16 and/or the second alignment layer 16A can beformed by a conventionally known method. For example, the alignmentlayer may be formed by a method in which a polyimide film is formed onthe glass substrate 14 and is then rubbed as described above, or amethod in which the glass substrate 14 is covered with a polymericcompound film that will become an optical alignment layer and polarizedUV (ultraviolet light) is applied to this film. An oriented PET(polyethylene terephthalate) film or the like may also be used to obtainthe alignment layer.

(Second Production Process)

Next, a production process in which a liquid crystalline polymer is usedto form a liquid crystal layer will be described by referring to FIGS.6(A) to 6(C).

In this production process, an alignment layer 16 is firstly formed on aglass substrate 14, as shown in FIG. 6(A), like in the aforementionedfirst production process.

As shown in FIG. 6(B), a liquid crystalline polymer 32 havingcholesteric regularity is applied to the alignment layer 16 and isoriented by the alignment-regulating action of the alignment layer 16.The liquid crystalline polymer 32 applied thus forms a liquid crystalphase.

Thereafter, as shown in FIG. 6(C), the liquid crystalline polymer 32 iscooled to a temperature equal to or lower than its glass transitiontemperature (Tg) to transform it into the glassy state, therebyobtaining a circularly-polarized-light-extracting optical element 30composed of a single liquid crystal layer.

In this production process, the liquid crystalline polymer 32 may bemade into a coating liquid by dissolving it in a solvent. If such acoating liquid is used, it is necessary to add, before the cooling step,the drying step of evaporating the solvent.

There may be used, as the liquid crystalline polymer, a cholestericliquid crystalline polymer itself having chirality, or a mixture of anematic liquid crystalline polymer and a cholesteric liquid crystallinepolymer.

The state of such a liquid crystalline polymer changes with temperature.For example, a liquid crystalline polymer having a glass transitiontemperature of 90° C. and an isotropic transition temperature of 200° C.is in the state of cholesteric liquid crystal at a temperature between90° C. and 200° C.; if this polymer is cooled to room temperature, it issolidified to the glassy state with its cholesteric structuremaintained.

If a cholesteric liquid crystalline polymer is used, the chiral power inthe liquid crystalline polymer may be adjusted by any known method inorder to control the incident light selective reflection wave range,which is determined by the cholesteric structure of the liquidcrystalline polymer. If a mixture of a nematic liquid crystallinepolymer and a cholesteric liquid crystalline polymer is used, the mixingratio of these two polymers may be adjusted for this purpose.

Also in this second production process, if the alignment layer 16 iswholly treated in advance so that its alignment-regulating action willact in substantially one direction, it is possible to align, insubstantially one direction, those liquid crystal line molecules thatare brought into contact with the alignment layer 16.

To make the director on the non-alignment-layer-side surface of theliquid crystal layer coincide with the direction in which thealignment-regulating action acts (i.e., the director on the surface ofthe liquid crystal layer that is in contact with the alignment layer16), the thickness of the liquid crystal layer may be made (½×integer)times the pitch of the molecular helix in the helical structureconsisting of the liquid crystalline molecules as mentioned previously,or a second alignment layer 16A as shown in FIG. 5 may be employed.

The aforementioned circularly-polarized-light-extracting opticalelements 10, 20 and 30 according to this embodiment of the inventionhave a single-layered structure composed of one liquid crystal layer.This embodiment is, however, not limited to this, and thecircularly-polarized-light-extracting optical element may be made tohave a multi-layered structure.

Specifically, like a circularly-polarized-light-extracting opticalelement 40 as shown in FIG. 7(E), a plurality of liquid crystal layers42 and 44 having cholesteric regularity with liquid crystallinemolecules in planar orientation may be directly and successivelylaminated. In this multi-layered circularly-polarized-light-extractingoptical element 40, the liquid crystal line molecules on one of the twomain opposite outermost surfaces of the liquid crystal layers 42 and 44laminated are wholly oriented in substantially one direction and theliquid crystalline molecules on the other main outermost surface arealso wholly oriented in substantially one direction, as shown in FIG. 1.In addition, it is preferable that the director on one of the two mainopposite outermost surfaces of the liquid crystal layers laminated besubstantially parallel to that on the other main outermost surface. By“substantially parallel” herein means that the discrepancy between thetwo directors is within the range of ±20°. In thiscircularly-polarized-light-extracting optical element 40, it ispreferable that the total thickness of the liquid crystal layers 42 and44 be made (½×integer) times the pitch of the molecular helix in thehelical structure consisting of the liquid crystalline molecules inorder to align the liquid crystalline molecules on one of the two mainopposite outermost surfaces of the liquid crystal layers 42 and 44laminated in precisely one direction and to align the liquid crystallinemolecules on the other outermost surface in precisely one direction. Itis also preferable that the directors in planes in the vicinity of theinterface of the two neighboring liquid crystal layers 42 and 44 besubstantially parallel to each other. The expression “substantiallyparallel” herein means that the discrepancy between the two directors iswithin the range of ±5°.

A process of producing a multi-layeredcircularly-polarized-light-extracting optical element will be describedhereinafter.

(First Production Process)

A production process of which polymerizable monomers or oligomers areused to form liquid crystal layers will firstly be explained byreferring to FIGS. 7(A) to 7(E).

In this production process, an alignment layer 16 is firstly formed on aglass substrate 14, as shown in FIG. 7(A). Polymerizable monomermolecules (or polymerizable oligomer molecules) 18 are then applied asliquid crystalline molecules to the alignment layer 16, as shown in FIG.7(B), thereby aligning these molecules by the alignment-regulatingaction of the alignment layer 16.

Polymerization of the polymerizable monomer (or polymerizable oligomer)18 is initiated with the molecular orientation maintained, by applyingultraviolet light with a photo polymerization initiator being added init, or by simply applying an electron beam, as shown in FIG. 7(C),thereby three-dimensionally crosslinking the polymerizable monomer (orpolymerizable oligomer) 18. The polymerizable monomer (or polymerizableoligomer) 18 is thus solidified to give a first liquid crystal layer 42.

As shown in FIG. 7(D), another polymerizable monomer (or polymerizableoligomer) 19 prepared separately is directly applied to the first liquidcrystal layer 42 that has been three-dimensionally cross-linked, and, asshown in FIG. 8, is aligned by the alignment-regulating action of thesurface of the three-dimensionally cross-linked first liquid crystallayer 42. To this polymerizable monomer (or polymerizable oligomer) 19,ultraviolet light is applied with a photopolymerization initiator beingadded in it, or an electron beam is simply applied, as shown in FIG.7(E), thereby three-dimensionally crosslinking the polymerizable monomer(or polymerizable oligomer) 19. The polymerizable monomer (orpolymerizable oligomer) 19 is thus solidified to give a second liquidcrystal layer 44, whereby a two-layeredcircularly-polarized-light-extracting optical element 40 is obtained.

To obtain a multi-layered circularly-polarized-light-extracting opticalelement composed of three or more layers, the above-described steps(FIGS. 7(D) and 7(E)) are repeated to successively laminate liquidcrystal layers in the number required.

Also in this production process, if the alignment layer 16 is whollytreated in advance so that its alignment-regulating action will act insubstantially one direction, it is possible to align, in substantiallyone direction, those liquid crystal line molecules that are brought intocontact with the alignment layer 16. In addition, a second alignmentlayer 16A as shown in FIG. 5 may be formed when the first liquid crystallayer 42 is solidified by conducting three-dimensional crosslinking,thereby aligning, in substantially one direction, the liquid crystalline molecules on the main surface of the liquid crystal layer 42 at theopposite of the alignment layer 16. In the production of a multi-layeredcircularly-polarized-light-extracting optical element composed of threeor more liquid crystal layers, the above procedure may be effected forthe second and later liquid crystal layers.

To make the directors on the two main opposite outermost surfaces of theliquid crystal layers 42 and 44 in thecircularly-polarized-light-extracting optical element 40 substantiallyparallel to each other, it is preferable to control the thickness of theliquid crystal layer 44 so that the director in the topmost plane in theliquid crystal layers will be substantially parallel to that in thelowermost plane in the liquid crystal layers, as shown in FIG. 3. Bydoing so, it is possible to more surely make the directors on the twomain opposite outermost surfaces parallel to each other.

(Second Production Process)

A production process in which liquid crystalline polymers are used toform liquid crystal layers will be described by referring to FIGS. 9(A)to 9(C).

In this production process, an alignment layer 16 is firstly formed on aglass substrate 14, as shown in FIG. 9(A), like in the above-describedfirst production process.

As shown in FIG. 9(B), a liquid crystalline polymer having cholestericregularity is applied to the alignment layer 16 and is aligned by thealignment-regulating action of the alignment layer 16. Thereafter, thisliquid crystalline polymer is cooled to a temperature equal to or lowerthan its glass transition temperature (Tg), thereby transforming it intothe glassy state to form a first liquid crystal layer 42′.

As shown in FIG. 9(C), another liquid crystalline polymer havingcholesteric regularity, separately prepared is directly applied to thefirst liquid crystal layer 42′ and is aligned by thealignment-regulating action of the surface of the first liquid crystallayer 42′ in the glassy state. This liquid crystalline polymer is thencooled to a temperature equal to or lower than its glass transitiontemperature (Tg) in the manner as described above, thereby transformingit into the glassy state to form a second liquid crystal layer 44′. Atwo-layered circularly-polarized-light-extracting optical element isthus obtained.

To obtain a multi-layered circularly-polarized-light-extracting opticalelement composed of three or more liquid crystal layers, theabove-described step (FIG. 9(C)) is repeated.

Also in this production process, if the alignment layer 16 is whollytreated in advance so that its the alignment-regulating action will actin substantially one direction, it is possible to align, insubstantially one direction, those liquid crystal line molecules thatare brought into contact with the alignment layer 16. In addition, asecond alignment layer 16A as shown in FIG. 5 may be formed when thefirst liquid crystal layer 42′ is solidified by conductingthree-dimensional crosslinking, thereby aligning, in substantially onedirection, the liquid crystal line molecules on the main surface of theliquid crystal layer 42′ at the opposite of the alignment layer 16. Inthe production of a multi-layered circularly-polarized-light-extractingoptical element composed of three or more layers, the above proceduremay be effected for the second and later liquid crystal layers.

To make the directors on the two main opposite outermost surfaces of theliquid crystal layers 42′ and 44′ in thecircularly-polarized-light-extracting optical element 40′ substantiallyparallel to each other, it is preferable to control the thickness of theliquid crystal layer 44′ so that the director in the topmost plane inthe liquid crystal layers will be substantially parallel to that in thelowermost plane in the liquid crystal layers, as shown in FIG. 3. Bydoing so, it is possible to more surely make the directors on the twomain outermost surfaces of the liquid crystal layers parallel to eachother.

The aforementioned circularly-polarized-light-extracting optical element10, 20, 30, 40 or 40′ according to this embodiment can be used, forinstance, in a polarized light source device 50 as shown in FIG. 10A.

As shown in FIG. 10A, in this polarized light source device 50, thecircularly-polarized-light-extracting optical element 10 (20, 30, 40 or40′) is arranged on the light-emitting-surface 52A side of a lightsource 52, so that it can receive light emitted from the light source 52and can transmit polarized light. The light source 52 is, for example, aflat illuminant and emits non-polarized white light from itslight-emitting surface 52A.

Therefore, in this polarized light source device 50, non-polarized lightemitted from the light source 52 is polarized by thecircularly-polarized-light-extracting optical element, and eitherright-handed or left-handed circularly polarized component having awavelength λ0 (see the above equation (1)) equal to the helical pitch ofthe liquid crystal having cholesteric regularity, in the range of a wavebandwidth Δλ (see the above equation (2)) is reflected; the othercircularly polarized component and non-polarized light in a wave rangeexcluding the reflection wave range are transmitted. Right-handed orleft-handed circularly polarized component in a specific wave range canthus be obtained. Practically, if non-polarized light in a wave rangeexcluding the wave range of the circularly polarized light transmittedis removed by the use of, for instance, a band pass filter, right-handedor left-handed circularly polarized component in a predetermined waverange can be obtained.

This polarized light source device 50 can be used, for example, as thelight source of a liquid crystal display 60, as shown in FIG. 10B.

As shown in FIG. 10B, this liquid crystal display 60 is composed of apolarized light source device 50 shown in FIG. 10A and a liquid crystalcell 62 that is arranged on the polarized-light-emitting-surface 50Aside of the polarized light source device 50 and that receives polarizedlight emitted from the polarized-light-emitting surface 50A of thepolarized light source device 50. The liquid cell 62 is fabricated sothat it can transmit polarized incident light in a certain wave rangewhile varying the transmittance for the light according to a voltageapplied, for instance, thereby displaying an image or the like.

Second Embodiment

The second embodiment of the present invention will be described byreferring to FIG. 11 to FIG. 20B.

A circularly-polarized-light-extracting optical element 110 according tothe first example of this embodiment will firstly be described byreferring to FIG. 11.

As shown in FIG. 11, this circularly-polarized-light-extracting opticalelement 110 includes a first liquid crystal layer 112, a second liquidcrystal layer 114 and a third liquid crystal layer 116, each havingcholesteric regularity, wherein these first to third liquid crystallayers 112, 114 and 116 are directly laminated in this order so that thehelical axes 118A of liquid crystal line molecules 118 will point insubstantially one direction (oriented in the direction of thickness ofthe liquid crystal layers). As diagrammatically shown in FIGS. 11, 12Aand 12B, in the first to third liquid crystal layers 112, 114 and 116,the director D of the liquid crystalline molecules 118 havingcholesteric regularity is continuously rotated in the direction of thethickness of the liquid crystal layers to form a helical structure.Further, in the first to third liquid crystal layers 112, 114 and 116,the directors D in planes in the vicinity of the interface of each twoneighboring liquid crystal layers (i.e., in the vicinity of theinterface 113 of the first liquid crystal layer 112 and the secondliquid crystal layer 114, and in the vicinity of the interface 115 ofthe second liquid crystal layer 114 and the third liquid crystal layer116) substantially coincide with each other. Cholesteric liquid crystalsor chiral nematic liquid crystals having cholesteric regularity, forexample, are used as the liquid crystalline molecules 118 in the firstto third liquid crystal layers 112, 114 and 116.

The first to third liquid crystal layers 112, 114 and 116 havingcholesteric regularity have the rotated-light-selecting property(polarized-light-separating property), that is, the property ofseparating a component optically rotated (circularly polarized) in onedirection from a component optically rotated in the opposite directionaccording to the physical orientation (planar orientation) of the liquidcrystalline molecules in the liquid crystal layer, as describedpreviously in the first embodiment.

That the directors D in planes in the vicinity of the interfaces 113 and115 of each two neighboring liquid crystal layers of the first to thirdliquid crystal layers 112, 114 and 116 substantially coincide with eachother means that the direction in which the liquid crystalline moleculeson the both sides of the interface 113 are aligned and that in which theliquid crystalline molecules on the both sides of the interface 115 arealigned are nearly equal to each other as shown in FIG. 12A or thatthese directions are different from each other by an angle ofapproximately 180° as shown in FIG. 12B. This is because, in many cases,the head of a liquid crystalline molecule is optically indistinguishablefrom its tail.

If the directors D in planes in the vicinity of the interfaces 113 and115 of each two neighboring liquid crystal layers of the first to thirdliquid crystal layers 112, 114 and 116 substantially coincide with eachother, discontinuity is never created in thecircularly-polarized-light-reflecting property, which is characteristicof the cholesteric structure, at these interfaces. If the two directorsD do not substantially coincide with each other, optical singularity isbrought about, and when the spectral transmittance is measured by theuse of circularly polarized light, discontinuity was observed in theselective reflection wavelength.

Whether or not the directors D substantially coincide with each othercan be known by observing the cross sections of the liquid crystallayers 112, 114 and 116 by a transmission electron microscope.Specifically, when the cross sections of the liquid crystal layers 112,114 and 116 having cholesteric regularity, in which the liquidcrystalline molecules are solidified, are observed by a transmissionelectron microscope, bright and dark stripes corresponding to the pitchof the molecular helix, characteristic of the cholesteric structure areobserved. If the bright and dark stripes that appear on the surface atwhich two neighboring liquid crystal layers are in contact with eachother, that is, the interface of these two liquid crystal layers, areseen uniformly in terms of concentration (brightness), it can be judgedthat the directors D in planes in the vicinity of the interface of thetwo neighboring liquid crystal layers substantially coincide with eachother.

To form the liquid crystal layers 112, 114 and 116 of thecircularly-polarized-light-extracting optical element 110, polymerizablemonomers or oligomers that can be three-dimensionally polymerized, aswell as liquid crystalline polymers can be used.

Examples of three-dimensionally crosslinkable, polymerizable monomersuseful for forming the liquid crystal layers include liquid crystallinemonomers and mixtures of chiral compounds as disclosed in JapaneseLaid-Open Patent Publication No. 258638/1995 and Published JapaneseTranslation No. 508882/1998 of PCT International Publication. Examplesof polymerizable oligomers that can be used to form the liquid crystallayers include cyclic organopolysiloxane compounds having cholestericphases as disclosed in Japanese Laid-Open Patent Publication No.165480/1982. By “three-dimensional crosslinking” is herein meant thatpolymerizable monomer or oligomer molecules are three-dimensionallypolymerized to give a network structure. If such a network structure isformed, the liquid crystalline molecules in the cholesteric liquidcrystalline state are optically fixed as they are, and a film that iseasy to handle as an optical film and that is stable at normaltemperatures can be obtained.

Examples of liquid crystalline polymers useful for forming the liquidcrystal layers include polymers having mesogen group, which makes thepolymers liquid crystalline, in their main chain or side chains, or bothmain chain and side chains, polymeric cholesteric liquid crystals havingcholesteryl group in their side chains, and liquid crystalline polymersas disclosed in Japanese Laid-Open Patent Publications No. 133810/1997and No. 293252/1999.

Next, a process of producing the circularly-polarized-light-extractingoptical element 110 according to this embodiment, having theabove-described constitution will be described hereinafter.

(First Production Process)

First of all, a production process in which polymerizable monomers oroligomers are used for forming liquid crystal layers will be describedby referring to FIGS. 13(A) to 13(E).

In this production process, an alignment layer 112 is firstly formed ona glass substrate 120, as shown in FIG. 13(A). Polymerizable monomermolecules (or polymerizable oligomer molecules) 112 a are then appliedas liquid crystalline molecules to the alignment layer 112, as shown inFIG. 13(B), thereby aligning these molecules by the alignment-regulatingaction of the alignment layer 112.

Next, polymerization of the polymerizable monomer (or polymerizableoligomer) 112 a is initiated with the molecular orientation maintained,by applying ultraviolet light with a photopolymerization initiator init, or by simply applying an electron beam, as shown in FIG. 13(C),thereby three-dimensionally crosslinking (polymerizing) and solidifyingthe polymerizable monomer molecules (or polymerizable oligomermolecules) 112 a. The polymerizable monomer (or polymerizable oligomer)112 a is thus solidified to give a liquid crystal layer 112.

As shown in FIG. 13(D), another polymerizable monomer (or polymerizableoligomer) 114 a prepared separately is then directly applied to thefirst liquid crystal layer 112 that has been three-dimensionallycross-linked. These liquid crystalline molecules applied are aligned onthe surface of the first liquid crystal layer 112 by thealignment-regulating action of the surface of the three-dimensionallycross-linked first liquid crystal layer 112.

In the above process, the mutual interaction between the surface of thethree-dimensionally cross-linked liquid crystal layer 112 and thepolymerizable monomer molecules (or polymerizable oligomer molecules)114 a, liquid crystalline molecules, used to form a second liquidcrystal layer 114 is significant. Namely, it is necessary that, when theliquid crystal line molecules in the first and second liquid crystallayers 112 and 114 come close to each other, the director D in the firstliquid crystal layer and the director D in the second liquid crystallayer become substantially equal to each other or become different fromeach other by an angle of approximately 180°. If the two directors D donot substantially coincide with each other, optical singularity isbrought about, and when spectral transmittance is measured by the use ofcircularly polarized light, discontinuity is observed in the selectivereflection wavelength.

Lastly, as shown in FIG. 13(E), the layer of the polymerizable monomer(or polymerizable oligomer) 114 a is three-dimensionally crosslinked andis solidified by applying ultraviolet light with a photopolymerizationinitiator being added, or by simply applying an electron beam, therebyforming a second liquid crystal layer 114. A two-layeredcircularly-polarized-light-extracting optical element 110 is thusobtained.

To obtain a multi-layered circularly-polarized-light-extracting opticalelement 110 composed of three or more liquid crystal layers, theabove-described steps (FIGS. 13(D) and 13(E)) are repeated tosuccessively laminate liquid crystal layers in the number required.

The polymerizable monomers (or polymerizable oligomers) 112 a and 114 amay be made into coating liquids by dissolving them in solvents. If suchcoating liquids are used, it is necessary to add the drying step ofevaporating the solvents before the step of three-dimensionallycrosslinking the polymerizable monomers (or polymerizable oligomers) 112a and 114 a by the application of ultraviolet light or an electron beam.

In the case where the polymerizable monomers (or polymerizableoligomers) 112 a and 114 a are made into liquid crystal layers atprescribed temperatures, the liquid crystal layers are nematic. If anychiral agent is added to these nematic liquid crystals, chiral nematicliquid crystals (cholesteric liquid crystals) can be obtained.Specifically, it is preferable to add a chiral agent to thepolymerizable monomer or oligomer in an amount of several to 10%. Byvarying the chiral power by changing the type of the chiral agent to beadded, or by varying the concentration of the chiral agent, it ispossible to control the selective reflection wave range, which isdetermined by the cholesteric structure of the polymerizable monomer oroligomer.

The alignment layer 122 can be formed by a conventionally known method.For example, the alignment layer may be formed by a method in which apolyimide film is formed on the glass substrate 120 and is then rubbedas described above, or a method in which the glass substrate 120 iscovered with a polymeric compound film that will become an opticalalignment layer and polarized UV (ultraviolet light) is applied to thisfilm. An oriented PET (polyethylene terephthalate) film or the like mayalso be used to obtain the alignment layer.

Further, it is also possible to use a light-transmitting substrateinstead of the glass substrate 120. In this case, there may be used asheet- or plate-like flat member made from a light-transmitting materialselected from homopolymers or copolymers of acrylic or methacrylicesters such as polymethyl methacrylate and polymethyl acrylate,polyesters such as polyethylene terephthalate, transparent resins suchas polycarbonate and polyethylene, and transparent ceramics.

(Second Production Process)

Next, a production process in which liquid crystalline polymers are usedto form liquid crystal layers will be described by referring to FIGS.14(A) to 14(C).

In this production process, an alignment layer 122 is firstly formed ona glass substrate 120, as shown in FIG. 14(A), like in theaforementioned first production process.

As shown in FIG. 14(B), a liquid crystalline polymer having cholestericregularity is applied to the alignment layer 122 and is oriented by thealignment-regulating action of the alignment layer 122. This liquidcrystalline polymer is then cooled to a temperature equal to or lowerthan its glass transition temperature (Tg); the polymer is thustransformed into the glassy state to give a first liquid crystal layer124.

Thereafter, as shown in FIG. 14(C), another liquid crystalline polymerhaving cholesteric regularity, separately prepared, is directly appliedto the first liquid crystal layer 124 and is oriented by thealignment-regulating action of the surface of the first liquid crystallayer 124 in the glassy state.

In the above process, the mutual interaction between the surface of theliquid crystal layer 124 in the glassy state and the liquid crystallinepolymer used for forming a second liquid crystal layer 126 issignificant. Namely, it is necessary that the director D in the firstliquid crystal layer 124 and the director D in the second liquid crystallayer 126 become substantially equal to each other or become differentfrom each other by an angle of approximately 180° when the liquidcrystal line molecules in the two liquid crystal layers come close toeach other. When the two directors D do not substantially coincide witheach other, optical singularity is brought about, and discontinuity isobserved in the selective reflection wavelength when spectraltransmittance is measured by the use of circularly polarized light.

Lastly, the liquid crystalline polymer is cooled to a temperature equalto or lower than its glass transition temperature (Tg) to transform itinto the glassy state in the manner as described above, thereby forminga second liquid crystal layer 126. Thus, a two-layeredcircularly-polarized-light-extracting optical element 120′ is obtained.

To obtain a multi-layered circularly-polarized-light-extracting opticalelement composed of three or more liquid crystal layers, theabove-described step (FIG. 14(C)) is repeated to successively laminateliquid crystal layers in the number required.

In this production process, the liquid crystalline polymers may be madeinto coating liquids by dissolving them in solvents. If such coatingliquids are used, it is necessary to add, before the cooling step, thedrying step of evaporating the solvents.

There may be used, as the liquid crystalline polymers, cholestericliquid crystalline polymers themselves having chirality, or mixtures ofnematic liquid crystalline polymers and cholesteric liquid crystallinepolymers.

The state of such liquid crystalline polymers changes with temperature.For example, a liquid crystalline polymer having a glass transitiontemperature of 90° C. and an isotropic transition temperature of 200° C.is in the state of cholesteric liquid crystal at a temperature between90° C. and 200° C.; if this polymer is cooled to room temperature, it issolidified to the glassy state with its cholesteric structuremaintained.

If a cholesteric liquid crystalline polymer is used, the chiral power inthe liquid crystalline polymer may be adjusted by any known method tocontrol the incident light selective reflection wave range, which isdetermined by the cholesteric structure of the liquid crystallinepolymer. If a mixture of a nematic liquid crystalline polymer and acholesteric liquid crystalline polymer is used, the mixing ratio ofthese two polymers may be adjusted for this purpose.

When coating a liquid crystal layer that has been solidified into theglassy state with another liquid crystalline polymer and aligning it, itis necessary to conduct heating. When the first and second liquidcrystal layers 124 and 126 are heated for this purpose, they areintermingled if they have substantially the same glass transitiontemperature and substantially the same isotropic transition temperature.It is therefore preferable to make the glass transition temperatures andthe isotropic transition temperatures of the two liquid crystal layersslightly different from each other.

Next, by referring to FIG. 15, a circularly-polarized-light-extractingoptical element 130 according to the second example of this embodimentwill be described.

In the circularly-polarized-light-extracting optical element 130, thepitch p1 of the molecular helix in the first liquid crystal layer 132formed in the above-described manner and the pitch p2 of the molecularhelix in the second liquid crystal layer 134 formed in theabove-described manner are different from each other, as shown in FIG.15.

The pitch of the molecular helix herein means the distance p1 or p2 ittakes for the director to rotate through 360° about the central axis(helical axis) of the molecular helix (see FIG. 15).

If the liquid crystal layers 132 and 134 are made different in the pitchof the molecular helix, the resultingcircularly-polarized-light-extracting optical element can extractcircularly polarized light having different wavelengths; this means thatthe waveband width is increased.

Next, by referring to FIG. 16, a circularly-polarized-light-extractingoptical element 140 according to the third example of this embodimentwill be described.

As shown in FIG. 16, this circularly-polarized-light-extracting opticalelement 140 comprises three layers of first to third liquid crystallayers 142, 144 and 146 laminated in the manner as described above.These liquid crystal layers 142, 144 and 146 are different in the pitchof the molecular helix, so that they reflect circularly polarized lighthaving different wavelengths λ1, λ2 and λ3.

FIG. 16 shows the following case: the directions of rotation of theliquid crystalline molecules in the respective liquid crystal layers142, 144 and 146 are the same, and the liquid crystal layers 142, 144and 146 reflect a part of right-handed circularly polarized component Rand transmit left-handed circularly polarized component L.

For instance, if the thickness required for a liquid crystal layer toreflect a circularly polarized component with a maximum reflectance isequivalent to 8 pitches of the molecular helix, each liquid crystallayer 142, 144 or 146 is made to have a thickness smaller than this,equivalent to 6.4 pitches. Namely, the thickness of each liquid crystallayer 142, 144 or 146 is made smaller than the thickness required forthe liquid crystal layer to reflect, with a maximum reflectance, eitherright-handed or left-handed circularly polarized component of lighthaving a specific wavelength, contained in incident light.

Non-polarized light incident on such liquid crystal layers 142, 144 and146 having cholesteric regularity is polarized, and, according to thepreviously mentioned property of separating polarized light, eitherright-handed or left-handed circularly polarized component of light in awave range with a center wavelength of λ0, having a waveband width of Δλis reflected, and the other circularly polarized component and light(non-polarized light) in a wave rage excluding the reflection wave rangeare transmitted. The right-handed or left-handed circularly polarizedcomponent is reflected without undergoing phase inversion unlike in thecase of ordinary reflection of light.

To reflect either right-handed or left-handed circularly polarizedcomponent with a maximum reflectance (generally from 95 to 99%) and totransmit the other component, a liquid crystal layer is generallyrequired to have a thickness equivalent to at least 8 pitches of themolecular helix.

The thickness of each liquid crystal layer 142, 144 or 146 shown in FIG.16 is, however, equivalent to 6.4 pitches, which is smaller than theabove-described pitches required.

It is therefore possible to make each liquid crystal layer reflect 80%of either right-handed or left-handed circularly polarized component andtransmit 20% of the same in the above-described range of waveband widthΔλ. With respect to the other circularly polarized component, eachliquid crystal layer transmits this component with a transmittance ofnearly 100%, higher than the transmittance attained by a liquid crystallayer whose thickness is equivalent to 8 pitches of the molecular helix.

Further, for example, if the thickness of each liquid crystal layer 142,144 or 146 is made equivalent to 5.6 pitches, it is possible to makeeach liquid crystal layer reflect 70% of either right-handed orleft-handed circularly polarized component and transmit 30% of the same.Namely, reflectance and transmittance in any percentages of the maximumreflectance can be obtained by changing the number of turns of themolecular helix in each liquid crystal layer 142, 144 or 146.

Furthermore, to reflect either right-handed or left-handed circularlypolarized component with a maximum reflectance (generally from 95 to99%) and to transmit the other component, a liquid crystal layer isgenerally required to have a thickness of at least 1.6 μm for visiblelight having a wavelength of 380 nm and a thickness of at least 3.3 μmfor visible light having a wavelength of 780 nm.

On the contrary, each liquid crystal layer 142, 144 or 146 shown in FIG.16 is made to have a thickness ranging from 1.24 μm (380 nm) to 2.6 μm(780 nm) (the thickness of each liquid crystal layer is linearly variedwith the selective reflection wavelength), which is smaller than theabove-described thickness required.

Therefore, in the above-described range of waveband width Δλ, it ispossible to make each liquid crystal layer reflect 80% of eitherright-handed or left-handed circularly polarized component and transmit20% of the same. With respect to the other circularly polarizedcomponent, each liquid crystal layer transmits the component with atransmittance of nearly 100%, higher than the transmittance attained bya liquid crystal layer having a thickness of 5 μm.

If the thickness of each liquid crystal layer 142, 144 or 146 is made,for example, from 1.1 μm (380 nm) to 2.3 μm (780 nm) (the thickness ofeach liquid crystal layer is linearly varied with the selectivereflection wavelength), it is possible to make the liquid crystal layerreflect 70% of either right-handed or left-handed circularly polarizedcomponent and transmit 30% of the same. Namely, reflectance andtransmittance in any percentages of the maximum reflectance can beobtained by changing the thickness of each liquid crystal layer 142, 144or 146.

In addition, since the thickness of each liquid crystal layer in thecircularly-polarized-light-extracting optical element 160 is madesmaller than the thickness required for the liquid crystal layer toreflect, with a maximum reflectance, either right-handed or left-handedcircularly polarized component, the same circularly polarized lightcomponent as reflected light can be obtained even from light enteringthe liquid crystal layer from the side opposite to incident light thatwill be reflected and outgoing from the liquid crystal layer.

In the circularly-polarized-light-extracting optical element 140 shownin FIG. 16, the first to third liquid crystal layers 142, 144 and 146reflect light having different wavelengths. The embodiment, however, isnot limited to this.

Specifically, like a circularly-polarized-light-extracting opticalelement 150 according to the fourth example of this embodiment as shownin FIG. 17, for example, first to third liquid crystal layers 152, 154and 156 may be made so that they reflect light having the samewavelength. In this circularly-polarized-light-extracting opticalelement 150, the second liquid crystal layer 154 reflects a part ofleft-handed circularly polarized component L; this liquid crystal layeris different, in this respect, from the first and third liquid crystallayers 152 and 156 which reflect a part of right-handed circularlypolarized component R.

By providing such liquid crystal layers, right-handed and left-handedcircularly polarized components in a specific wave range can besimultaneously extracted in any percentages.

Next, a circularly-polarized-light-extracting optical element 160according to the fifth example of this embodiment will be described byreferring to FIG. 18.

As shown in FIG. 18, this circularly-polarized-light-extracting opticalelement 160 comprises a transition liquid crystal layer 166 providedbetween a first liquid crystal layer 162 and a second liquid crystallayer 164, the pitch of the molecular helix in the first liquid crystallayer 162 being different from that of the molecular helix in the secondliquid crystal layer 164.

In this circularly-polarized-light-extracting optical element 160, thepitch p1 of the molecular helix in the first liquid crystal layer 162,the pitch p2 of the molecular helix in the second liquid crystal layer164 and the pitch ps of the molecular helix in the transition liquidcrystal layer 166 are made to fulfil the following conditions: p1<p2,and p1≦ps≦p2.

Namely, the pitch ps of the molecular helix in the transition liquidcrystal layer 166 is varied in the direction of thickness so that, atthe interface 163 of the first liquid crystal layer 162 and thetransition liquid crystal layer 166, ps will be equal to p1 and that, atthe interface 165 of the second liquid crystal layer 164 and thetransition liquid crystal layer 166, ps will be equal to p2 .Specifically, the first liquid crystal layer 162 is allowed to slightlymelt when it is coated with the second liquid crystal layer 164. Bydoing so, it becomes possible to extract circularly polarized light in acontinuously broadened wave range.

In the case where liquid crystal layers having different pitches arelaminated like in the case of the circularly-polarized-light-extractingoptical element 130 shown in FIG. 15, it is preferable to make theselective reflection wave ranges of at least two liquid crystal layerspartially overlapped, as shown in FIG. 19. Namely, it is preferable tomake at least two of the liquid crystal layers laminated have selectivereflection wave ranges whose center regions C1 and C2 do not coincidewith each other and whose end regions E1 and E2 are partiallyoverlapped. By doing so, it becomes possible to extract circularlypolarized light in a continuously broadened wave range.

The aforementioned circularly-polarized-light-extracting optical element110, 130, 140, 150 or 160 according to this embodiment can be used in apolarized light source device 180 as shown in FIG. 20A, for example.

As shown in FIG. 20A, in this polarized light source device 180, thecircularly-polarized-light-extracting optical element 184 (110, 130,140, 150 or 160) is arranged on the light-emitting-surface 182A side ofa light source 182, so that it can receive light emitted from the lightsource 182 and can transmit polarized light. The light source 182 is,for example, a flat illuminant and emits non-polarized white light fromits light-emitting surface 182A.

Therefore, in this polarized light source device 180, non-polarizedlight emitted from the light source 182 is polarized by thecircularly-polarized-light-extracting optical element, and eitherright-handed or left-handed circularly polarized component having awavelength λ0 (see the above equation (1)) equal to the helical pitch ofthe liquid crystal having cholesteric regularity, in the range ofwaveband width Δλ (see the above equation (2)) is reflected; the othercircularly polarized component and non-polarized light in a wave rangeexcluding the reflection wave range are transmitted. Right-handed orleft-handed circularly polarized component in a specific wave range canthus be obtained. Practically, if non-polarized light in a wave rangeexcluding the wave range of the circularly polarized light transmittedis removed by the use of, for instance, a band pass filter, right-handedor left-handed circularly polarized component in a predetermined waverange can be obtained.

This polarized light source device 180 can be used, for example, as thelight source of a liquid crystal display 190 as shown in FIG. 20B.

As shown in FIG. 20B, this liquid crystal display 190 is composed of apolarized light source device 180 shown in FIG. 20A and a liquid crystalcell 192 that is arranged on the polarized-light-emitting-surface 180Aside of the polarized light source device 180 and that receivespolarized light emitted from the polarized-light-emitting surface 180Aof the polarized light source device 180. The liquid cell 192 isfabricated so that it can transmit polarized incident light in a certainwave range while varying the transmittance for the light according to,for instance, a voltage applied, thereby displaying an image or thelike.

EXAMPLES First Examples

The aforementioned first embodiment of the invention will be explainedby referring to the following Examples and Comparative Examples.

Example 1-1

In Example 1-1, a single liquid crystal layer was made from apolymerizable monomer, where the thickness of the liquid crystal layerwas made uniform to orient the liquid crystalline molecules in onedirection.

90 parts of a monomer containing, in its molecule, polymerizableacrylates at both ends and spacers between mesogen existing at thecenter and the acrylates, having a nematic-isotropic transitiontemperature of 110° C., and 10 parts of a chiral gent having, in itsmolecule, polymerizable acrylates at both ends were dissolved intoluene. To this toluene solution was added a photopolymerizationinitiator in an amount of 5% by weight of the above monomer. (Withrespect to the chiral nematic liquid crystal thus obtained, it wasconfirmed that the liquid crystalline molecules would be oriented on analignment layer in one direction that was the direction, in which thealignment layer had been rubbed, ±5 degrees.)

Separately, a transparent glass substrate was spin-coated with polyimidedissolved in a solvent. After drying, a film of the polyimide was formedat 200° C. (film thickness 0.1 μm) and was rubbed in a definitedirection so that this film would function as an alignment layer.

The glass substrate provided with this alignment layer was set in aspin-coater; and the alignment layer was spin-coated with theabove-prepared toluene solution under such conditions that the thicknessof the resulting film would be as uniform as possible.

The toluene contained in the toluene solution applied was thenevaporated at 80° C. to form a coating film on the alignment layer. Itwas visually confirmed by way of selective reflection of light that thiscoating film was cholesteric.

Ultraviolet light was applied to the above coating film to cause thephotopolymerization initiator contained in the coating film to generateradicals, by which the acrylates in the monomer molecules werepolymerized by three-dimensional crosslinking, thereby obtaining asingle-layered circularly-polarized-light-extracting optical element.The thickness of the coating film was 2 μm±1.5%. By the measurement madeby using a spectrophotometer, it was confirmed that the centerwavelength of the selective reflection wave range of the coating filmwas 600 nm.

Further, the circularly-polarized-light-extracting optical element thusobtained was placed between two circular polarizers arranged in thecross nicol disposition, as shown in FIG. 21, and was visually observed.The bright and darks stripes observed on the displaying area were veryfew.

Comparative Example 1-1

In Comparative Example 1-1, a single liquid crystal layer was made froma polymerizable monomer, where the thickness of the liquid crystal layerwas made non-uniform to cause the liquid crystalline molecules to pointin different directions. Namely, a circularly-polarized-light-extractingoptical element was produced in the same manner as in Example 1-1,provided that the thickness of the coating film was made 2 μm±5% bychanging the conditions under which spin coating was conducted. Thiscircularly-polarized-light-extracting optical element was observed inthe same manner as in Example 1-1. As a result, it was found that brightand dark stripes clearly appeared on the displaying area.

Comparative Example 1-2

In Comparative Example 1-2, a single liquid crystal layer was formed byusing a polymerizable monomer on an alignment layer that had been rubbedin not one direction, thereby causing the liquid crystalline moleculesto point in different directions. Namely, acircularly-polarized-light-extracting optical element was produced inthe same manner as in Example 1-1, provided that the alignment layer wasrubbed in a random fashion. This circularly-polarized-light-extractingoptical element was observed in the same manner as in Example 1-1. As aresult, it was found that bright and dark stripes clearly appeared onthe displaying area.

Example 1-2

In Example 1-2, a single liquid crystal layer was made from apolymerizable monomer, where the thickness of the liquid crystal layerwas made uniform and the pitch of the molecular helix was adjusted sothat the directors on the two main opposite surfaces of the liquidcrystal layer would be parallel to each other. Namely, acircularly-polarized-light-extracting optical element was produced inthe same manner as in Example 1-1, provided that the liquid crystallayer was made, by making use of the refractive index of the materialused for forming the liquid crystal layer, to have such a thickness thatthe director at the starting point of the cholesteric structure would beparallel to the director at the end point of the cholesteric structure.This circularly-polarized-light-extracting optical element was observedin the same manner as in Example 1-1. As a result, it was obvious thatthe bright and dark stripes observed on the displaying area were fewerthan those stripes that appeared when a liquid crystal layer formedwithout controlling thickness and helical pitch as described above wasused.

Example 1-3

In Example 1-3, a plurality of liquid crystal layers were made from apolymerizable monomer, where the total thickness of the liquid crystallayers was made uniform to orient the liquid crystalline molecules inone direction.

The circularly-polarized-light-extracting optical element produced inExample 1-1 was used as a first liquid crystal layer. The surface ofthis first liquid crystal layer at the opposite of the alignment layerwas spin-coated, at a number of revolutions greater than before, withthe same toluene solution as that used in Example 1-1 except that theamount of the chiral agent was 15 parts.

Next, the toluene contained in the toluene solution was evaporated at80° C. to form a coating film on the first liquid crystal layer. It wasvisually confirmed by way of selective reflection of light that thiscoating film was cholesteric. By the measurement made by using aspectrophotometer, it was confirmed that the center wavelength of theselective reflection wave range of this coating film was approximately500 nm.

Ultraviolet light was applied to the above coating film to cause thephotopolymerization initiator contained in the coating film to generateradicals, by which the acrylates in the monomer molecules werepolymerized by three-dimensional crosslinking to form a second liquidcrystal layer. A multi-layered circularly-polarized-light-extractingoptical element was thus obtained. The total thickness of this opticalelement was found to be 3.5 μm±1.5%.

The cross section of this multi-layeredcircularly-polarized-light-extracting optical element was observed by atransmission electron microscope. As a result, it was found thefollowing: the bright and dark stripes that appeared between thepolymerized liquid crystal layers were parallel to each other (fromthis, it can be known that the directions of the helical axes of theliquid crystalline molecules in the liquid crystal layers are the same);and no discontinuity was present between the liquid crystal layers (fromthis, it can be known that the directors in planes in the vicinity ofthe interface of the two neighboring liquid crystal layers coincide witheach other).

Further, the circularly-polarized-light-extracting optical element wasplaced between two circular polarizers arranged in the cross nicoldisposition, as shown in FIG. 21, and was visually observed. The brightand dark stripes observed on the displaying area were very few.

Comparative Example 1-3

In Comparative Example 1-3, a plurality of liquid crystal layers weremade from a polymerizable monomer, where the total thickness of theliquid crystal layers was made non-uniform to cause the liquid crystalline molecules to point in different directions. Namely, acircularly-polarized-light-extracting optical element was produced inthe same manner as in Example 1-3, provided that the total thickness ofthe liquid crystal layers was made 3.5 μm±5% by changing the conditionsunder which spin coating was conducted. Thiscircularly-polarized-light-extracting optical element was observed inthe same manner as in Example 1-3. As a result, it was found that brightand dark stripes clearly appeared on the displaying area.

Example 1-4

In Example 1-4, a plurality of liquid crystal layers were made fromliquid crystalline polymers, where the total thickness of the liquidcrystal layers were made uniform to orient the liquid crystallinemolecules in one direction.

A toluene solution was prepared by dissolving, in toluene, a liquidcrystalline polymer containing acrylic side chains, having a glasstransition temperature of 80° C. and an isotropic transition temperatureof 200° C. (With respect to the polymeric cholesteric liquid crystalthus obtained, it was confirmed that the molecules would be oriented onan alignment layer in one direction that was the direction, in which thealignment layer had been rubbed, ±5 degrees.)

Separately, a transparent glass substrate was spin-coated with polyimidedissolved in a solvent. After drying, a film of the polyimide was formedat 200° C. (film thickness 0.1 μm) and was rubbed in a definitedirection so that this film would function as an alignment layer.

The glass substrate provided with this alignment layer was set in aspin-coater; and the alignment layer was spin-coated with theabove-prepared toluene solution under such conditions that the resultingfilm would be as uniform as possible.

The toluene contained in the toluene solution applied was thenevaporated at 90° C. to form, on the alignment layer, a coating film,which was held at 150° C. for 10 minutes. It was visually confirmed byway of selective reflection of light that this coating film wascholesteric. The coating film was cooled to room temperature totransform the liquid crystalline polymer into the glassy state and tofix the liquid crystalline polymer in this state, thereby forming afirst liquid crystal layer. The thickness of the first liquid crystallayer was 2 μm±1.5%. By the measurement made by using aspectrophotometer, it was confirmed that the center wavelength of theselective reflection wave range of the first liquid crystal layer was600 nm.

Further, the first liquid crystal layer in the glassy state wasspin-coated, at a number of revolutions greater than before, with atoluene solution prepared by dissolving, in toluene, a liquidcrystalline polymer containing acrylic side chains, having a glasstransition temperature of 75° C. and an isotropic transition temperatureof 190° C.

Next, the toluene contained in the toluene solution was evaporated at80° C. to form a coating film on the first liquid crystal layer. It wasvisually confirmed by way of selective reflection of light that thiscoating film was cholesteric. By the measurement made by using aspectrophotometer, it was confirmed that the center wavelength of theselective reflection wave range of the coating film was approximately500 nm.

Thereafter, the toluene contained in the toluene solution applied wasevaporated at 90° C.; and the coating film was held at 150° C. for 10minutes. It was visually confirmed by way of selective reflection oflight that this coating film was cholesteric. The coating film wascooled to room temperature to transform the liquid crystalline polymerinto the glassy state and to fix the liquid crystalline polymer in thisstate, thereby forming a second liquid crystal layer. A multi-layeredcircularly-polarized-light-extracting optical element was thus obtained.The total thickness of this circularly-polarized-light-extractingoptical element was 3.5 μm±1.5%.

The cross section of this multi-layeredcircularly-polarized-light-extracting optical element was observed by atransmission electron microscope. As a result, it was found thefollowing: the bright and dark stripes that appeared between thesolidified liquid crystal layers were parallel to each other (from this,it can be known that the directions of the helical axes of the liquidcrystalline molecules in the liquid crystal layers are the same); and nodiscontinuity was present between the liquid crystal layers (from this,it can be known that the directors in planes in the vicinity of theinterface of the two neighboring liquid crystal layers coincide witheach other). In the measurement made by using a spectrophotometer, nooptical singularity was observed in the transmittance.

Further, the circularly-polarized-light-extracting optical element thusobtained was placed between two circular polarizers arranged in thecross nicol disposition, as shown in FIG. 21, and was visually observed.The bright and dark stripes observed on the displaying area were veryfew.

Comparative Example 1-4

In Comparative Example 1-4, a plurality of liquid crystal layers weremade from liquid crystalline polymers, where the total thickness of theliquid crystal layers was made non-uniform to cause the liquidcrystalline molecules to point in various directions. Namely, acircularly-polarized-light-extracting optical element was produced inthe same manner as in Example 1-4, provided that the total thickness ofthe liquid crystal layers was made 3.5 μm±5% by changing the conditionsunder which spin coating was conducted. This multi-layeredcircularly-polarized-light-extracting optical element was observed inthe same manner as in Example 1-4. As a result, it was found that brightand dark stripes clearly appeared on the displaying area.

Second Examples

The second embodiment of the present invention will now be explained byreferring to the following Examples and Comparative Example.

Example 2-1

In Example 2-1, a plurality of liquid crystal layers were made from apolymerizable monomer, where the directors in planes in the vicinity ofthe interface of each two neighboring liquid crystals were made tocoincide with each other by rubbing process.

90 parts of a monomer containing, in its molecule, polymerizableacrylates at both ends and spacers between mesogen existing at thecenter and the acrylates, having a nematic-isotropic transitiontemperature of 110° C., and 10 parts of a chiral gent having, in itsmolecule, polymerizable acrylates at both ends were dissolved intoluene. To this toluene solution was added a photopolymerizationinitiator in an amount of 5% by weight of the above monomer. (Withrespect to the chiral nematic liquid crystal thus obtained, it wasconfirmed that the liquid crystalline molecules would be oriented on analignment layer in one direction that was the direction in which thealignment layer had been rubbed ±5degrees.)

Separately, a transparent glass substrate was spin-coated with polyimidedissolved in a solvent. After drying, a film of the polyimide was formedat 200° C. (film thickness 0.1 μm) and was rubbed in a definitedirection so that this film would function as an alignment layer.

The glass substrate provided with this alignment layer was set in aspin-coater; and the alignment layer was spin-coated with theabove-prepared toluene solution.

The toluene contained in the toluene solution applied was thenevaporated at 80° C. to form a coating film on the alignment layer. Itwas visually confirmed by way of selective reflection of light that thiscoating film was cholesteric.

Ultraviolet light was applied to the above coating film to cause thephotopolymerization initiator contained in the coating film to generateradicals, by which the acrylates in the monomer molecules werepolymerized by three-dimensional crosslinking, thereby forming a firstliquid crystal layer (thickness 2 μm). By the measurement made by usinga spectrophotometer, it was confirmed that the center wavelength of theselective reflection wave range of the first liquid crystal layer wasapproximately 600 nm.

Further, the surface of the polymerized first liquid crystal layer wasrubbed in the same direction as that of the director on this surface.The direction of the director on the first liquid crystal layer can beknown by calculation from the direction in which the alignment layer hasbeen rubbed, and the selective reflection wavelength, refractive indexand thickness of the cholesteric liquid crystal, or by opticalmeasurement. It can also be known by observing the cross section of theliquid crystal layer by a transmission electron microscope.

The first liquid crystal layer that had been rubbed was spin-coated, ata number of revolutions greater than before, with the same toluenesolution as the above-described one except that the amount of the chiralagent was 15 parts.

The toluene contained in the toluene solution applied was thenevaporated at 80° C. to form a coating film on the first liquid crystallayer. It was visually confirmed by way of selective reflection of lightthat this coating film was cholesteric. By the measurement made by usinga spectrophotometer, it was confirmed that the center wavelength of theselective reflection wave range of this coating film was approximately500 nm.

Ultraviolet light was applied to the above coating film to cause thephotopolymerization initiator contained in the coating film to generateradicals, by which the acrylates in the monomer molecules werepolymerized by three-dimensional crosslinking, thereby forming a secondliquid crystal layer (thickness 1.5 μm). A multi-layeredcircularly-polarized-light-extracting optical element was thus produced.

The cross section of this multi-layeredcircularly-polarized-light-extracting optical element was observed by atransmission electron microscope. As a result, it was found thefollowing: the bright and dark stripes that appeared between thepolymerized liquid crystal layers were parallel to each other (fromthis, it can be known that the directions of the helical axes of theliquid crystalline molecules in the liquid crystal layers are the same);and no discontinuity was present between the liquid crystal layers (fromthis, it can be known that the directors in planes in the vicinity ofthe two neighboring liquid crystal layers coincide with each other). Inthe measurement made by using a spectrophotometer, no opticalsingularity was observed in the transmittance.

Comparative Example 2-1

In Comparative Example 2-1, a plurality of liquid crystal layers weremade from a polymerizable monomer, where the directors in planes in thevicinity of the interface of each two neighboring liquid crystal layerswere made different from each other by rubbing process. Namely, theprocedure of Example 2-1 was repeated, provided that the surface of thepolymerized coating film was rubbed in the direction perpendicular tothe director on the coating film.

The cross section of the multi-layeredcircularly-polarized-light-extracting optical element thus obtained wasobserved by a transmission electron microscope. As a result, it wasfound the following: the bright and dark stripes that appeared betweenthe liquid crystal layers were parallel to each other (from this, it canbe known that the directions of the helical axes of the liquidcrystalline molecules in the liquid crystal layers are the same), butdiscontinuity was present between the liquid crystal layers (from this,it can be known that the directors in planes in the vicinity of theinterface of the two neighboring liquid crystal layers do not coincidewith each other). In the measurement made by using a spectrophotometer,optical singularity was observed in the transmittance. From the detailedobservation, the state of circular polarization was found disordered.

Example 2-2

In Example 2-2, a plurality of liquid crystal layers were made from apolymerizable monomer, where the liquid crystal layers were directlylaminated so that the directors in planes in the vicinity of theinterface of each two neighboring liquid crystal layers would coincidewith each other.

The procedure of Example 2-1 was repeated, provided that the surface ofthe polymerized coating film was not rubbed.

The cross section of the multi-layeredcircularly-polarized-light-extracting optical element thus obtained wasobserved by a transmission electron microscope. As a result, it wasfound the following: the bright and dark stripes that appeared betweenthe polymerized liquid crystal layers were parallel to each other (fromthis, it can be known that the directions of the helical axes of theliquid crystalline molecules in the liquid crystal layers are the same);and no discontinuity was present between the liquid crystal layers (fromthis, it can be known that the directors in planes in the vicinity ofthe interface of the two neighboring liquid crystal layers coincide witheach other). In the measurement made by using a spectrophotometer, nooptical singularity was observed in the transmittance.

Example 2-3

In Example 2-3, a plurality of liquid crystal layers were made fromliquid crystalline polymers, where the liquid crystal layers weredirectly laminated so that the directors in planes in the vicinity ofthe interface of each two neighboring liquid crystal layers wouldcoincide with each other.

A toluene solution was prepared by dissolving, in toluene, a liquidcrystalline polymer containing acrylic side chains, having a glasstransition temperature of 80° C. and an isotropic transition temperatureof 200° C. (With respect to the polymeric cholesteric liquid crystalthus obtained, it was confirmed that the liquid crystalline moleculeswould be oriented on an alignment layer in one direction that was thedirection, in which the alignment layer had been rubbed, ±5 degrees.)

Separately, a transparent glass substrate was spin-coated with polyimidedissolved in a solvent. After drying, a film of the polyimide was formedat 200° C. (film thickness 0.1 μm) and was rubbed in a definitedirection so that this film would function as an alignment layer.

The glass substrate provided with this alignment layer was set in aspin-coater; and the alignment layer was spin-coated with theabove-prepared toluene solution.

The toluene contained in the toluene solution applied was thenevaporated at 90° C. to form, on the alignment layer, a coating film,which was held at 150° C. for 10 minutes. It was visually confirmed byway of selective reflection of light that this coating film wascholesteric. The coating film was cooled to room temperature totransform the liquid crystalline polymer into the glassy state and tofix the liquid crystalline polymer in this state, thereby forming afirst liquid crystal layer (thickness 2 μm). By the measurement made byusing a spectrophotometer, it was confirmed that the center wavelengthof the selective reflection wave range of the first liquid crystal layerwas approximately 600 nm.

Further, the first liquid crystal layer in the glassy state wasspin-coated, at a number of revolutions greater than before, with atoluene solution prepared by dissolving, in toluene, a liquidcrystalline polymer containing acrylic side chains, having a glasstransition temperature of 75° C. and an isotropic transition temperatureof 190° C.

Next, the toluene contained in the toluene solution applied wasevaporated at 80° C. to form a coating film on the first liquid crystallayer. It was visually confirmed by way of selective reflection of lightthat this coating film was cholesteric. By the measurement made by usinga spectrophotometer, it was confirmed that the center wavelength of theselective reflection wave range of the coating film was approximately500 nm.

Thereafter, the toluene contained in the toluene solution applied wasevaporated at 90° C.; and the coating film was held at 150° C. for 10minutes. It was visually confirmed by way of selective reflection oflight that this coating film was cholesteric. The coating film wascooled to room temperature to transform the liquid crystalline polymerinto the glassy state and to fix the liquid crystalline polymer in thissate, thereby forming a second liquid crystal layer (thickness 1.5 μm).A multi-layered circularly-polarized-light-extracting optical elementwas thus obtained.

The cross section of this multi-layeredcircularly-polarized-light-extracting optical element was observed by atransmission electron microscope. As a result, it was found thefollowing: the bright and dark stripes that appeared between thesolidified liquid crystal layers were parallel to each other (from this,it can be known that the directions of the helical axes of the liquidcrystalline molecules in the liquid crystal layers are the same); and nodiscontinuity was present between the liquid crystal layers (from this,it can be known that the directors in planes in the vicinity of theinterface of the two neighboring liquid crystal layers coincide witheach other). In the measurement made by using a spectrophotometer, nooptical singularity was observed in the transmittance.

Example 2-4

In Example 2-4, a transition liquid crystal layer was provided betweentwo neighboring liquid crystal layers of multiple liquid crystal layersmade from a polymerizable monomer.

90 parts of a monomer containing, in its molecule, polymerizableacrylates at both ends and spacers between mesogen existing at thecenter and the acrylates, having a nematic-isotropic transitiontemperature of 110° C., and 10 parts of a chiral gent having, in itsmolecule, polymerizable acrylates at both ends were dissolved intoluene. To this toluene solution was added a photopolymerizationinitiator in an amount of 3% by weight of the above monomer. (Withrespect to the chiral nematic liquid crystal thus obtained, it wasconfirmed that the liquid crystalline molecules would be oriented on analignment layer in one direction that was the direction, in which thealignment layer had been rubbed, ±5 degrees.)

Separately, a transparent glass substrate was spin-coated with polyimidedissolved in a solvent. After drying, a film of the polyimide was formedat 200° C. (film thickness 0.1 μm) and was rubbed in a definitedirection so that this film would function as an alignment layer.

The glass substrate provided with this alignment layer was set in aspin-coater; and the alignment layer was spin-coated with theabove-prepared toluene solution.

The toluene contained in the toluene solution applied was thenevaporated at 80° C. to form a coating film on the alignment layer. Itwas visually confirmed by way of selective reflection of light that thiscoating film was cholesteric.

Ultraviolet light was applied to the above coating film in an amount of{fraction (1/10)} of that of ultraviolet light applied in Example 2-1 tocause the photopolymerization initiator contained in the coating film togenerate radicals, by which the acrylates in the monomer molecules werepolymerized by three-dimensional crosslinking, thereby forming a firstliquid crystal layer (thickness 2 μm). By the measurement made by usinga spectrophotometer, it was confirmed that the center wavelength of theselective reflection wave range of the first liquid crystal layer wasapproximately 600 nm.

Further, the polymerized first liquid crystal layer was spin-coated, ata number of revolutions greater than before, with the same toluenesolution as the above-described one except that the amount of the chiralagent was 15 parts.

Next, the toluene contained in the toluene solution was evaporated at80° C. to form a coating film on the first liquid crystal layer. It wasvisually confirmed by way of selective reflection of light that thiscoating film was cholesteric. By the measurement made by using aspectrophotometer, it was confirmed that the center wavelength of theselective reflection wave range of this coating film was approximately500 nm.

Ultraviolet light was applied to the above coating film to cause thephotopolymerization initiator contained in the coating film to generateradicals, by which the acrylates in the monomer molecules werepolymerized by three-dimensional crosslinking, thereby forming a secondliquid crystal layer (thickness 1.5 μm). A multi-layeredcircularly-polarized-light-extracting optical element was thus obtained.

The cross section of this multi-layeredcircularly-polarized-light-extracting optical element was observed by atransmission electron microscope. As a result, it was found thefollowing: the bright and dark stripes that appeared between thepolymerized liquid crystal layers were parallel to each other (fromthis, it can be known that the directions of the helical axes of theliquid crystalline molecules in the liquid crystal layers are the same);and no discontinuity was present between the liquid crystal layers (fromthis, it can be known that the directors in planes in the vicinity ofthe two neighboring liquid crystal layers coincide with each other). Inthe measurement made by using a spectrophotometer, no opticalsingularity was observed in the transmittance.

It was also confirmed that a transition layer was present between thetwo liquid crystal layers. The pitch of the bright and dark stripesoriginating from this transition layer was equal to that of the brightand dark stripes originating from the liquid crystal layers betweenwhich the transition layer was present.

The reason why the transition layer was created seems to be as follows:since the photopolymerization initiator was added in a decreased amountand ultraviolet light was applied also in a decreased amount, the firstliquid crystal layer was not fully three-dimensionally cross-linked, andthe components of the first liquid crystal layer were partiallytransferred to the second liquid crystal layer.

1. A circularly-polarized-light-extracting optical element comprising aliquid crystal layer having cholesteric regularity with liquidcrystalline molecules in planar orientation, wherein the liquidcrystalline molecules located on one of the two main opposite surfacesof the liquid crystal layer are wholly oriented in substantially onedirection so as to have a specific director in a plane of one mainsurface, and the liquid crystalline molecules located on the other mainsurface of the liquid crystal layer are also wholly oriented insubstantially one direction so as to have a specific director in a planeof the other main surface.
 2. The circularly-polarized-light-extractingoptical element according to claim 1, wherein the director on one of thetwo main opposite surfaces of the liquid crystal layer is substantiallyparallel to that on the other main surface of the liquid crystal layer.3. The circularly-polarized-light-extracting optical element accordingto claim 2, wherein a helical structure consisting of liquid crystallinemolecules with helical turns in a number of (0.5×integer) is presentbetween the liquid crystalline molecules existing on the two mainopposite surfaces of the liquid crystal layer.
 4. A polarized lightsource device comprising: a light source; and acircularly-polarized-light-extracting optical element according to claim1, which receives light emitted from the light source and transmitpolarized light.
 5. A liquid crystal display comprising: a polarizedlight source device according to claim 4; and a liquid crystal cell thatreceives polarized light emitted from the polarized light source deviceand transmits the polarized light while changing a transmittance for it.6. A circularly-polarized-light-extracting optical element comprising aplurality of liquid crystal layers having cholesteric regularity withliquid crystalline molecules in planar orientation, the liquid crystallayers being successively and directly laminated, wherein the liquidcrystalline molecules located on one of the two main opposite outermostsurface of the liquid crystal layers laminated are wholly oriented insubstantially one direction so as to have a specific director in a planeof one main surface, and the liquid crystalline molecules located on theother main outermost surface of the laminated liquid crystal layers arealso wholly oriented in substantially one direction so as to have aspecific director in a plane of the other main surface.
 7. Thecircularly-polarized-light-extracting optical element according to claim6, wherein the director on one of the two main opposite outermostsurfaces of the liquid crystal layers laminated is substantiallyparallel to that on the other main outermost surface of the liquidcrystal layers laminated.
 8. The circularly-polarized-light-extractingoptical element according to claim 7, wherein a helical structureconsisting of liquid crystalline molecules with helical turns in anumber of (0.5×integer) is present between the liquid crystallinemolecule existing on the two main outermost surfaces of the liquidcrystal layers laminated.
 9. The circularly-polarized-light-extractingoptical element according to claim 6, wherein the directors in planes ina vicinity of an interface of each two neighboring liquid crystal layersof the multiple liquid crystal layers are substantially parallel to eachother.
 10. A process of producing acircularly-polarized-light-extracting optical element comprising thesteps of: coating an alignment layer whose entire surface has beentreated so that its alignment-regulating action will act insubstantially one direction, with liquid crystalline moleculescomprising polymerizable monomer or oligomer molecules havingcholesteric regularity, so as to align the liquid crystalline moleculesby the alignment-regulating action of the alignment layer;three-dimensionally crosslinking the liquid crystalline molecules thathave been aligned by the alignment-regulating action of the alignmentlayer, thereby forming a first liquid crystal layer; directly coatingthe first liquid crystal layer with another liquid crystalline moleculescomprising polymerizable monomer or oligomer molecules havingcholesteric regularity, so as to align the liquid crystalline moleculesby the alignment-regulating action of the surface of the first liquidcrystal layer that has been three-dimensionally crosslinked; andthree-dimensionally crosslinking the liquid crystalline molecules thathave been aligned by the alignment-regulating action of the surface ofthe three-dimensionally crosslinked first liquid crystal layer, therebyforming a second liquid crystal layer.
 11. The process of producing acircularly-polarized-light-extraction optical element according to claim10, wherein a thickness of the first liquid crystal layer and that ofthe second liquid crystal layer are adjusted so that the directors onthe two main opposite surfaces of the first liquid crystal layer will besubstantially parallel to each other and that the directors on the twomain opposite surfaces of the second liquid crystal layer will besubstantially parallel to each other.
 12. Then process of producing acircularly-polarized-light-extracting optical element according to claim10, wherein, in the step of coating the alignment layer with the liquidcrystalline molecules and aligning the liquid crystalline molecules toform the first liquid crystal layer, the alignment of the liquidcrystalline molecules on the surface of the first liquid crystal layeris regulated by applying another alignment layer to the surface of thefirst liquid crystal layer at the opposite of the firstly providedalignment layer.
 13. A process of producing acircularly-polarized-light-extracting optical element comprising thesteps of: coating an alignment layer whose entire surface has beentreated so that its alignment-regulating action will act insubstantially one direction, with a liquid crystalline polymer havingcholesteric regularity, so as to align the liquid crystalline polymer bythe alignment-regulating action of the alignment layer; cooling theliquid crystalline polymer that has been aligned by thealignment-regulating action of the alignment layer to transform it intothe glassy state, thereby forming a first liquid crystal layer; directlycoating the first liquid crystal layer with another liquid crystallinepolymer having cholesteric regularity, so as to align the liquidcrystalline polymer by the alignment-regulating action of the surface ofthe first liquid crystal layer that has been transformed into the glassystate; and cooling the liquid crystalline polymer that has been alignedby the alignment-regulating action of the surface of the first liquidcrystal layer in the glassy state to transform it into the glassy state,thereby forming a second liquid crystal layer.
 14. The process ofproducing a circularly-polarized-light-extracting optical elementaccording to claim 13, wherein a thickness of the first liquid crystallayer and that of the second liquid crystal layer are adjusted sothatthe directors on the two main opposite surface of the first liquidcrystal layer will be substantially parallel to each other and that thedirectors on the two main opposite surfaces of the second liquid crystallayer will be substantially parallel to each other.
 15. The process ofproducing a circularly-polarized-light-extracting optical elementaccording to claim 13, wherein, in the step of coating the alignmentlayer with the liquid crystalline polymer and aligning the liquidcrystalline polymer to form the first liquid crystal layer, thealignment of the liquid crystalline polymer on the surface of the firstliquid crystal layer is regulated by applying another alignment layer tothe surface of the first liquid crystal layer at the opposite of thefirstly provided alignment layer.
 16. Acircularly-polarized-light-extracting optical element comprising aplurality of liquid crystal layers having cholesteric regularity,wherein the liquid crystal layers are laminated so that helical axes ofliquid crystalline molecules will point in substantially one directionand that directors in planes in a vicinity of an interface of each twoneighboring liquid crystal layers of the multiple liquid crystal layerswill substantially coincide with each other.
 17. Thecircularly-polarized-light-extracting optical element according to claim16, wherein each liquid crystal layer comprises polymerizable monomer oroligomer molecules that have been three-dimensionally crosslinked. 18.The circularly-polarized-light-extracting optical element according toclaim 16, wherein each liquid crystal layer comprises a liquidcrystalline polymer.
 19. The circularly-polarized-light-extractingoptical element according to claim 16, wherein at least one of themultiple liquid crystal layers has a pitch of a molecular helix in ahelical structure consisting of liquid crystalline molecules, differentfrom that of a molecular helix in a helical structure in the otherliquid crystal layers.
 20. The circularly-polarized-light-extractingoptical element according to claim 16, wherein a thickness of eachliquid crystal layer is smaller than a thickness required for the liquidcrystal layer to reflect, with a maximum reflectance, eitherright-handed or left-handed circularly polarized component of lighthaving a specific wavelength, contained in incident light.
 21. Thecircularly-polarized-light-extracting optical element according to claim16, wherein the directions of rotation of the liquid crystallinemolecules in the respective liquid crystal layers are the same.
 22. Thecircularly-polarized-light-extracting optical element according to claim21, wherein at least two of the multiple liquid crystal layers haveselective reflection wave ranges whose center regions do not agree witheach other and whose end regions are partially overlapped.
 23. Apolarized light source device comprising: a light source; and acircularly-polarized-light-extracting optical element according to claim16, which receives light emitted from the light source and transmitspolarized light.
 24. A liquid crystal display comprising: a polarizedlight source device according to claim 23; and a liquid crystal cellthat receives polarized light emitted from the polarized light sourcedevice and transmits the polarized light while changing a transmittancefor it.
 25. A circularly-polarized-light-extracting optical elementcomprising: a plurality of liquid crystal layers having cholestericregularity; and a transition liquid crystal layer provided between atleast any two neighboring liquid crystal layers of the multiple liquidcrystal layers, in which a pitch of a molecular helix in a helicalstructure consisting of liquid crystalline molecules varies in adirection of thickness, wherein the liquid crystal layers are laminatedso that helical axes of liquid crystalline molecules in the respectiveliquid crystal layers will point in substantially one direction;directors in planes in a vicinity of an interface of each twoneighboring liquid crystal layers of the multiple liquid crystal layerssubstantially coincide with each other; a pitch of a molecular helix inone of the two liquid crystal layers between which the transition liquidcrystal layer is provided is different from that of a molecular helix inthe other liquid crystal layer; and the pitch of the molecular helix onone surface of the transition liquid crystal layer is substantiallyequal to that of the molecular helix in the liquid crystal layer whichis in contact with one surface of the transition liquid crystal layer,while the pitch of the molecular helix on the other surface of thetransition liquid crystal layer is substantially equal to that of themolecular helix in the other liquid crystal layer which is in contactwith the other surface of the transition liquid crystal layer.
 26. Aprocess of producing a circularly-polarized-light-extracting opticalelement comprising the steps of: coating an alignment layer with liquidcrystalline molecule comprising polymerizable monomer or oligomermolecules having cholesteric regularity, so as to align the liquidcrystalline molecules by the alignment-regulating action of thealignment layer; three-dimensionally crosslinking the liquid crystallinemolecules that have been aligned by the alignment-regulating action ofthe alignment layer, thereby forming a first liquid crystal layer;directly coating the first liquid crystal layer with another liquidcrystalline molecules comprising polymerizable monomer or oligomermolecules having cholesteric regularity, so as to align the liquidcrystalline molecules by the alignment-regulating action of the surfaceof the first liquid crystal layer that has been three-dimensionallycrosslinked; and three-dimensionally crosslinking the liquid crystallinemolecules that have been aligned by the alignment-regulating action ofthe surface of the three-dimensionally crosslinked first liquid crystallayer, thereby forming a second liquid crystal layer.
 27. A process ofproducing a circularly-polarized-light-extracting optical elementcomprising the steps of: coating an alignment layer with a liquidcrystalline polymer having cholesteric regularity, so as to align theliquid crystalline polymer by the alignment-regulating action of thealignment layer; cooling the liquid crystalline polymer that has beenaligned by the alignment-regulating action of the alignment layer totransform it into the glassy state, thereby forming a first liquidcrystal layer; directly coating the first liquid crystal layer withanother liquid crystalline polymer having cholesteric regularity, so asto align the liquid crystalline polymer by the alignment-regulatingaction of the surface of the first liquid crystal layer that has beentransformed into the glassy state; and cooling the liquid crystallinepolymer that has been aligned by the alignment-regulating action of thesurface of the first liquid crystal layer in the glassy state totransform it into the glassy state, thereby forming a second liquidcrystal layer.